C 

e 


THE  THEORY 


OF    THE 


GAS  ENGINE. 


By  DTJGALD    CLERK. 


REPRINTED  FROM  VAN 


NEW  YOKE: 
D.   VAN  NOSTRAND,  PUBLISHER, 

23  MURRAY  AND  27  WARREN  STREET. 

1882 


PRE  F  AC  E. 


The  continued  existence  of  the  Gas 
Engine  as  a  competitor  with  the  Steam, 
and  Hot  Air  Engines  is  no  longer  an 
open  question.  It  has  fairly  passed 
that  phase  of  the  experimental  stage 
which  determines  its  fitness  to  aid  in 
the  solution  of  the  ^problem  of  the  eco- 
nomical conversion  of  heat  into  mechan- 
ical work.- 

The  improvements  of  the  last  few  years 
have  brought  this  motor  into  a  conspicu- 
ous position. 

We  believe  this  essay  of  Mr.  Clerk's  to 
be  the  best  presentation  of  the  theory  of 
tke  Gas  Engine  that  has  yet  appeared. 

EDITOR  OF  MAGAZINE. 


The  Theory  of  the  Gas  Engine. 

THE  practical  problem  of  the  conver- 
sion of  heat  into  mechanical  work  has 
long  occupied  the  minds  of  engineers 
and  scientists ;  the  steam  engine  is  a 
partial  solution,  but  although  perfect  as 
a  machine,  its  efficiency  is  so  low  that  it 
can  hardly  be  considered  as  satisfactory 
and  final.  As  the  result  of  the  best 
modern  practice  it  may  be  taken  that  the 
steam  engine  does  not  convert  more  than 
10  per  cent,  of  the  heat  used  by  it  into 
work,  and  this  in  engines  of  considerable 
size  and  with  boilers  and  furnaces  fairly 
efficient.  In  small  engines  it  is  much 
less,  indeed  it  is  certain  that  few  among 
the  thousands  of  steam  engines  in  daily 
use  below  6  HP.  give  an  efficiency  greater 
than  4  per  cent.  The  great  cause  of  loss 
is  the  amount  of  heat  necessary  to  change 
the  water  from  the  liquid  to  the  gaseous 


state,  most  of  this  heat  being  rejected 
with  the  exhaust  either  into  the  conden- 
ser or  the  atmosphere.  Many  attempts 
have  been  made  to  use  liquids  of  lower 
specific  heat  than  water,  and  requiring 
less  heat  for  evaporation,  the  principal 
being  alcohol,  ether  and  carbon  bisul- 
phide, but  for  obvious  reasons  no  success 
has  been  attained. 

To  heated  air  as  a  means  of  obtaining 
power,  the  objection  of  loss  by  latent 
heat  does  not  apply,  the  air  is  already  in 
the  gaseous  statej  and  any  heat  added  at 
constant  volume  increases  the  tempera- 
ture, and  therefore  the  pressure2  without 
the  complication  of  change  of  physical 
state.  A  high  efficiency  would  therefore 
be  expected,  and  according  to  Professor 
Rankine  the  efficiency  of  the  fluid  in  the 
engines  of  the  "Ericsson"  was  about 
0.26  ;  the  efficiency  of  the  furnace  was 
however  low,  and  accordingly  the  actual 
efficiency  oc  the  engine  was  no  higher 
than  that  of  the  best  steam  engines  now 
in  use.  In  the  "  Stirling"  hot-air  engine, 
he  found  the  efficiency  of  the  fluid  to  be 


0.3  with  a  higher  efficiency  of  furnace 
than  in  Ericsson's. 

In  the  Ericsson  engine  the  air  was 
heated  at  constant  pressure,  the  volume 
augmenting  ai\d  the  power  being  given 
by  the  increased  volume  of  the  air  as  it 
entered  the  motor  cylinder  from  the  re- 
servoir into  which  it  had  been  compress- 
ed. The  mean  effective  pressure  was 
only  2.12  Ibs.  on  the  square  inch ;  the 
size  and  friction  of  the  engine  for  a  given 
power  was  enormous.  In  the  Stirling 
engine  the  air  was  heated  at  constant 
volume  with  increase  in  pressure,  the 
power  being  obtained  by  subsequent  ex- 
pansion ;  the  mean  available  pressure 
was  37  Ibs.  per  square  inch,  and  the  fric- 
tion of  the  engine  only  amounted  to  one- 
tenth  of  the  total  indicated  power.  Both 
engines  used  the  now  well  known  contri- 
vance, the  regenerator,  which  was  the 
invention  of  Dr.  Stirling,  and  which  is 
the  cause  in  both  of  the  high  efficiency. 

The  failure  of  these  engines  was  due 
to  the  rapid  burning  out  of  the  cylinder 
bottoms  by  the  direct  action  of  the  fire, 


it  being  found  impossible  to  heat  the  air 
rapidly  enough  to  the  required  tempera- 
ture without  maintaining  the  temperature 
of  the  metal  surfaces  much  higher  than 
the  maximum  temperature  to  be  attained 
by  the  air.  To  overcome 'this  slow  heat- 
ing of  the  air  when  in  mass  has  been  the 
object  of  many  inventors,  and  a  type  has 
often  been  proposed  with  a  closed  fur- 
nace, and  the  air  forced  through  this 
furnace  keeping  up  the  combustion,  the 
hot  products  going  to  the  motor  cylinder 
and  there  doing  work.  This  method  of 
internal  heating,  however,  introduces  dif- 
ficulties as  grave  as  exist  in  the  external 
method.  The  hot  gases  having  to  pass 
through  pipes  and  valves  to  the  motor 
cylinder  renders  it  impossible  to  main- 
tain a  very  high  temperature  without 
damage  to  the  machine.  Sir  George 
Cay  ley  was  the  first  to  make  and  work 
experimentally  an  engine  of  this  type. 

In  view  of  these  futile  attempts,  until 
very  recently  hot  air  was  considered  as 
among  the  failures  of  the  past,  and  it 
was  believed  that,  imperfect  as  the  steam 


9 

engine  is,  nothing  was  likely  to  succeed 
in  producing  a  better  result. 

The  great  progress  made  in  recent 
years  with  the  gas  engine,  and  its  advance 
from  the  state  of  an  interesting  but 
troublesome  toy  to  a  practic-el  powerful 
rival  of  the  steam  engine,  has  shown  that 
air  may  after  all  be  the  chief  motive 
power  of  the  future.  In  the  gas  engine 
chemical  considerations  greatly  modify 
the  theory  and  prevent  it  from  ranking 
as  a  simple  hot-air  engine;  but  to  be 
thoroughly  understood  it  is  better  first 
to  consider  the  power  to  be  obtained 
from  air  under  certain  theoretical  condi- 
tions. 

Three  well  defined  types  of  engines 
have  been  proposed — 

(1.)  An  engine  drawing  into  its  cylin- 
der gas  and  air  at  atmospheric  pressure 
for  a  portion  of  its  stroke,  cutting  off 
communication  with  the  outer  atmos- 
phere, and  immediately  igniting  the  mix- 
ture, the  piston  being  pushed  forward 
by  the  pressure  of  the  ignited  gases 
during  the  remainder  of  its  stroke.  The 


10 

in-stroke  then  discharges  the  products 
of  combustion. 

(2.)  An  engine  in  which  a  mixture  of 
gas  and  air  is  drawn  into  a  pump,  and 
is  discharged  by  the  return  stroke  into 
a  reservoir  in  a  state  of  compression. 
From  the  reservoir  the  mixture  enters 
into  a  cylinder,  being  ignited  as  it  en- 
ters, without  rise  in  pressure,  but  simply 
increased  in  volume,  and  following  the 
piston  as  it  moves  forward,  the  return 
stroke  discharges  the  products  of  com- 
bustion. 

(3.)  An  engine  in  which  a  mixture  of 
gas  and  air  is  compressed  or  introduced 
under  compression  into  a  cylinder,  or 
space  at  the  end  of  a  cylinder,  and  then 
ignited  while  the  volume  remains  con- 
stant and  the  pressure  rises.  Under  this 
pressure  the  piston  moves  forward,  and 
the  return  stroke  discharges  the  exhaust. 

Several  minor  types  have  been  pro- 
posed and  many  modifications  of  these 
three  methods  are  used.  A  thorough 
understanding  of  these,  however,  renders 


11 

it  possible  to  judge  the  merits  of  any 
other. 

Types  1  and  3  are  explosion  engines, 
the  volume  of  the  mixture  remaining 
constant  while  the  pressure  increases. 
Type  2  is  a  gradual  combustion  engine 
in  which  the  pressure  is  constant  but 
the  volume  increases. 

The  author,  in  the  course  of  his  ex- 
periments on  gas  engines,  has  found  that 
13537°  Centigrade  is  the  temperature 
usually  attained  by  the  ignited  gases  in 
his  engine,  and  he  has  accordingly  in- 
vestigated' the  behaviour  of  air  under 
different  conditions  at  this  temperature. 

Type  1.  Suppose  an  engine  to  have  a 
piston  with  an  area  of  144  square  inches 
and  a  stroke  of  2  feet.  Let  the  piston 
move  through  the  first  half  of  its  stroke 
drawing  into  the  cylinder  air ;  let  enough 
heat  be  immediately  added  to  this  air  to 
cause  it  to  rise  instantly  to  1,537°  Centi- 
grade, and  the  piston  continue  moving 
forward  under  the  pressure  produced.  If 
there  be  no  loss  of  heat  through  the  sides 
of  the  cold  cylinder,  but  the  temperature 


12 


of  the  air  fall  only  through  performing 
work,  how  much  work  would  be  done 
when  the  piston  completes  its  out-stroke  ? 
The  air  before  the  heat  is  added  is 
supposed  to  be  at  a  temperature  of  17° 
Centigrade  (about  60°  Fahrenheit),  and 
the  ordinary  atmospheric  pressure.  In 
Fig.  1  the  line  marked  adiabatic  No.  2  is 
the  curve  showing  the  work  which  would 
be  obtained  under  the  supposed  condi- 
tions. Fig.  2.  is  the  indicator  diagram 
such  an  engine  would  furnish.  It  is  not 
necessary  here  to  detail  the  calculations. 
With  this  paper  is  given  a  table  of  the 
data  used,  so  that  the  numbers  may  be 
verified.  The  following  are  the  results : 


1  cubic  foot  of  air  (at  170°  Centigrade, " 
and  760  millimetres  mercury)  re- 
maining at  constant  volume  re- 
quires to  heat  it  to  1,537°  Centi- 
grade, an  amount  of  heat  equiva- 
lent to.. 


26,762 
foot-lbs. 


Maximum  pressure  in  Ibs .  per  square  j 
inch  above  atmosphere J      '    J 

Pressure  at  the  end  of  stroke  per  ) 

I.                     -i  r  19. b  Ibs. 

square  inch  above  atmosphere J 


OP  THK 


UNIVERSITY 


l== 


'ijouj  ajenbs  jsd'sqj  u;  ajnssajd  aj.n| 


14 

Mean  pressure  during  available  part )  ^  g  ^g 
of  stroke ) 

Temperature  of  air  at  the  end  of  )  -<  QQO°  n 
stroke ) 

Work  done  on  piston 5,731  foot-lbs. 

Duty  of  engine     '       =0.21. 

As  the  engine  is  supposed  to  draw  in 
air  for  half  of  its  stroke,  the  last  half  of 
the  stroke  only  is  utilized  for  power ;  the 
mean  available  pressure  calculated  for 

89  8 
the  whole  stroke  is  only— ~  =   19.9  Ibs. 

per  square  inch.  There  is  a  considerable 
pressure  at  the  end  of  the  stroke  which 
could  be  made  to  give  more  work  by  ex- 
panding further  ;  but  for  the  purpose  of 
comparison  it  is  better  to  consider  the 
three  types  of  engine  as  each  having  a 
cylinder  capacity  swept  by  the  piston  of 
2  cubic  feet,  and  in  each  case  using  in  its 
operation  1  cubic  foot  of  air  at  each 
stroke. 

Type  2.  Suppose  an  engine  to  draw 
into  a  pump  1  cubic  foot  of  air,  on  its 
return  stroke  forcing  the  air  into  a  reser- 
voir at  a  pressure  of  76.6  Ibs.  per  square 
inch  above  the  atmosphere.  The  motor 


15 


If! 


d 

b£> 


I  a 

•qoui  ej^nbs  jed-sq|  ui 
9j9C(dsouu;B   uodn  ejnsse 


16 

piston  is  now  at  the  beginning  of  its  out- 
stroke,  and  as  it  moves  forward  air  from 
the  reservoir  enters  the  cylinder,  but  as 
it  enters  it  is  heated  to  1,537°  Centigrade, 
without  rise  in  pressure ;  the  motor  pis- 
ton sweeps  through  2  cubic  feet. 

Fig.  3 -shows  the  indicated  card  of  this 
engine.  abed  is  the  pump  diagram. 
Air  at  17°  Centigrade  is  taken  in,  com- 
pressed without  loss*  of  heat,  the  temper- 
ature rising  under  the  compression  to 
217°.5  Centigrade.  When  it  is  equal  to 
the  pressure  in  the  reservoir  it  is  forced 
into  the  reservoir,  as  is  shown  on  the 
line  b  c. 

In  all  the  operations  no  loss  or  gain  of 
heat  is  assumed,  except  in  doing  work  or 
in  work  being  done  on  the  air.  In  the 
motor  diagram  from  c  to  E  the  air  is  flow- 
ing from  the  reservoir  following  the  pis- 
ton, and  the  temperature  is  1,537°  Centi- 
grade during  the  whole  admission.  At  e 
the  communication  with  the  reservoir  is 
cut  off,  and  the  temperature  falls  while 
the  air  is  expanding  doing  work,  until  it 
reaches  the  end  of  the  stroke,  when  tha 


17 


H 

->    u 
la 

{  9  «10  1  2  3  4  5  6  7 

1  cubic  foot  2 

• 

f 

/ 

I537?0 

7 

^) 

, 

/ 

/ 

. 

r 
1 

/ 

« 

- 

f* 

g       |        g        go    g      o  - 
•LJOUJ  ejisnbs  jed  -sq|  ui 

18 


exhaust  is    discharged    by    the    return 
stroke  of  the  piston. 

For  convenience  the  pump  diagram  is 
shown  on  the  motor  one,  and  the  shaded 
portion  represents  the  work  done  by  the 
air  as  the  result  of  the  cycle.  As  the 
heat  is  added  while  the  air  expands  in 
volume,'  it  takes  considerably  more  to 
raise  a  cubic  foot  of  air  to  the  required 
temperature  than  in  the  case  of  type  1. 

1  cubic  foot  of  air  (17°  Centigrade^) 
and  760  millimeters  mercury)  at  I 
constant  pressure  requires  to  heat  }-    32,723 
it  from  the  temperature  of  com-     foot-lbs. 
pression217°.5  to  l,537°Centigrade  I 
heat  equivalent  to J 

Maximum  pressure  inlbs.  per  square  )  ~Q  L 
inch  above  atmosphere ) 

Pressure  at  end  of  stroke  above  at- )  *  Q 
mosphere - ) 

Mean  pressure  during  available  )  47.1  Ibs.  per 
part  of  stroke f  square  inch. 

Temperature  of  air  at  the  end  of  )  $SL  1,089^ 
stroke J  Centigrade 

Work  done  on  piston 11,759  foot-lbs.  , 

Duty  of  engine  —^- -  =0.36. 


19 

Type  3.  Suppose  an  engine  to  draw 
into  a  pump  1  cubic  foot  of  air,  on  its 
return  stroke  forcing  it  into  a  reservoir 
at  a  pressure  of  40  Ibs.  above  the  atmos- 
phere. The  motor  piston  is  now  at  the 
beginning  of  its  out-stroke,  and  as  it 
moves  forward  air  from  the  reservoir 
enters  the  cylinder  while  the  piston 
sweeps  through  0.39  cubic  feet.  At  this 
point  communication  is  cut  off,  and  the 
temperature  suddenly  raised  to  1,537° 
Centigrade.  Hitherto  the  air  has  re- 
mained at  the  temperature  of  compres- 
sion 150°.  5.  The  pressure  goes  straight 
up  to  220  Ibs.  above  the  atmosphere. 
This  is  shown  at  Fig.  1,  and  also  at  Fig. 
4,  which  is  the  diagram  of  this  type  of 
engine.,  a  b  c  d  is  the  compression  dia- 
gram ;  a  b  e  f  the  motor  diagram.  The 
piston  continues  to  move  forward,  and 
the  air  expands  doing  work.  At  the  end 
of  the  stroke  the  pressure  has  fallen  to 
8.4  Ibs.  per  square  inch  above  the  atmos- 
phere. 


20 

1  cubic  foot  of  sir  (17°  Centigrade, 
and  760  millimeters  mercury)  at 
constant  volume  requires  to  heat  it 
from  the  temperature  of  compres- 


24,416 
foot-lbs. 


sion   150°.  5  Centigrade  to  1,537° 

Centigrade  heat,  equivalent  to  ---- 
Maximum  pressure  in  Ibs.  per  square 

inch  above  atmosphere  ............ 

Pressure  at  end  of  stroke  ............      8.4  Ibs. 

Mean  pressure  during  available  )  47.8  Ibs.  per 

part  of  stroke  ...............  [  square    inch. 

)  QRjO° 

Temperature  at  middle  of  stroke  £  (jenti£rade 
Temperature  at  end  of  stroke.  .  648°  Centigrade. 
Work  done  on  the  piston  _______  11,090  foot-lbs. 

11,090    , 
Duty  of  engine 


Fig.  5  shows  the  most  important  modi- 
fication of  this  type  ;  in  it,  instead  of  a 
separate  reservoir,  a  space  is  left  at  the 
end  of  the  cylinder,  into  which  the  piston 
does  not  enter,  and  in  this  space  is  com- 
pressed the  gases  forming  the  inflamma- 
ble mixture.  The  rise  in  pressure  there- 
fore commences  at  the  beginning  of  the 
stroke  instead  of  when  the  piston  has 
traveled  out.  In  this  diagram  the  volume 


21 


bJO 


1 

3>        D 

CN 

1 

10 
•<»< 

1 

I 

1 

/ 

cubic  foot. 

s 

/ 

1 

/  - 

• 

O 

-!« 

i 

/ 

i 

X 

°s 

2 

* 

^ 

O            O            C?            O           CO    O 

1      g      J3      2      S 
•qouiajBnbsr  J»d  'sq|  ui 

22 


swept  by  the  piston  and  the  clearance 
space  together  are  supposed  to  be  equal 
to  2  cubic  feet.  Comparing  the  results 
obtained  from  these  three  modes  under 
precisely  similar  conditions,  the  same 
weight  of  air  heated  to  the  same  degree, 
and  used  in  cylinders  of  identical  capa- 
city, there  is  a  considerable  difference  in 
the  results  possible  even  under  the 
purely  theoretic  conditions  stated. 

The  relative  work  obtained  from  1 
cubic  foot  of  air  heated  to  the  assumed 
temperature  is  shown  below. 

RESULTS  FROM  ENGINES   OF   EQUAL  VOLUME 
SWEPT   BY  MOTOR   PISTON. 

Type 

1.  5,731  foot-lbs.  work  obtained    0.21  duty. 

2.  11,759        '•          "  "  0.36     " 

3.  11,090        "          "  "          0.45     " 

That  is,  in  an  engine  of  type  1,  if  100 
heat-units  be  used,  21  units  will  be  con 
verted  into  mechanical  work.  In  type  2, 
with  the  same  amount  of  heat,  36  units 
will  be  given  as  work,  and  in  type  3  no 
less  than  45  units  would  be  converted 
into  work. 


23 


/ 

/ 

/ 

I 

o 

7f 

ri 

• 


-  e 


^      M 

i 


§    § 

•qouj  ajenbs  jed  -sq|  ui 


24 

The  great  advantage  of  compression 
over  no  compression  is  clearly  seen,  by 
the  simple  operation  of  compressing  be- 
fore heating ;  the  last  type  of  engine 
gives  for,  the  same  expenditure  of  heat 
2.1  times  as  much  work  as  the  first. 
Compression,  as  used  by  the  second 
type,  does  not  afford  so  favorable  a  re- 
sult ;  but  even  then  the  advantage  is 
apparent,  1.6  times  the  effect  being  pro- 
duced. By  a  greater  degree  of  compres- 
sion before  heating  even  better  results 
are  possible.  In  an  engine  of  type  3 
expanding  to  the  same  volume  after  igni- 
tion as  before  compression,  the  possible 
duty  D  is  determined  by  the  atmospheric 
absolute  temperature  T',  and  the  abso- 
lute temperature  after  compression  T;  it  is 

T— T' 

D=  — m~~  whatever  may  be  the  maxi- 
mum temperature  after  ignition.  In- 
creasing the  temperature  of  ignition  in- 
creases the  power  of  the  engine,  but 
does  not  cause  the  conversion  of  a 
greater  proportion  of  heat  into  work. 
With  any  given  maximum  temperature 


25 

the  smaller  the  difference  between  that 
temperature  and  the  temperature  of 
compression,  the  greater  is  the  propor- 
tion of  added  heat  converted  into  work 
with  any  given  amount  of  expansion. 
The  greater  the  compression  before  igni- 
tion, the  more  closely  the  two  tempera- 
tures come  together,  and  the  higher  is 
the  duty  of  the  engine  ;  neglecting  in  the 
meantime  the. practical  conditions  of  loss 
What  compression  does  is  to  enable  a 
great  fall  of  temperature  to  be  obtained 
due  to  work  done  with  but  a  small  move- 
ment of  the  piston.  In  type  1  when  the 
piston  has  reached  the  end  of  its  stroke, 
the  increase  from  the  moment  of  ignition 
is  only  from  one  volume  to  two  volumes, 
while  in  type  3  with  the  same  total 
volume  swept  by  the  piston,  it  increases 
from  one  volume  to  five  volumes.  In 
the  one  case  the  ratio  of  expansion  is 
two,  while  in  the  other  it  is  five.  This 
will  be  readily  seen  in  Figs.  2  and  4. 
Now  this  increased  expansion  is  not  ob- 
tained at  the  cost  of  loss  average  press- 
ure ;  in  type  1  the  mean  available  press- 


26 


ure  over  the  whole  stroke  is  nearly  20 
Ibs.  per  square  inch,  while  in  type  3  it  is 
38.5  Ibs.  per  square  inch  ;  that  is,  the 
compression  engine  for  equal  size  and 
piston  speed  has  nearly  twice  the  power 
of  the  other. 

In  the  compression  engine  with  a 
maximum  temperature  of  1,537°  Centi- 
grade, the  final  temperature  is  648° 
Centigrade,  while  in  the  other,  with  the 
same  maximum  temperature,  the  final 
temperature  is  1,089C  Centigrade.  It  is 
true  that  by  expanding  sufficiently  the 
same  final  temperature  can  be  obtained 
without  compression,  but  the  average 
pressure  will  be  low,  and  consequently 
less  available  for  the  production  of  power. 
To  produce  anything  like  an  expansion 
of  five  times  without  compression  the 
pressure  would  fall  below  the  atmos- 
phere, and  it  would  be  necessary  to  ex- 
pand into  a  partial  vacuum,  and  use  a 
condenser  and  vacuum  pump,  as  is  done 
in  the  steam  engine.  Compression  makes 
it  possible  to  obtain  from  heated  air  a 
great  amount  of  work  with  but  a  small 


27 

movement  of  piston,  the  smaller  volume 
giving  greater  pressures,  and  thus  ren- 
dering the  power  developed  more  mechani- 
cally available.  The  higher  the  maximum 
temperature  the  greater  the  amount  of 
compression  which  can  be  used  advan- 
tageously. There  is  a  degree  of  com- 
pression for  every  temperature,  beyond 
which  any  increase  causes  a  diminution 
of  the  power  of  the  engine  for  a  given 
size. 

The  compression  in  the  author's  engine 
is  40  Ibs.  per  square  inch  above  the  at- 
mosphere, and  he  has  accordingly  con- 
fined himself  to  the  comparison  of 
engines  employing  this  amount  of  com- 
pression with  those  using  no  compres- 
sion. Now,  seeing  that  this  difference 
is  produced  between  engines  of  types  1 
and  3  by  the  simple  difference  of  cycle, 
when  there  is  no  loss  of  heat  through 
the  sides  of  the  cylinder,  the  question 
arises  which  engine  would  give  the  great- 
est effect,  which,  engine  in  actual  prac- 
tice, with  a  cylinder  kept  cold  by  water, 
-would  come  nearest  to  theory  ?  In  which 


28 

of  the  engines  would  there  be  the  smaller 
loss  of  heat  ? 

The  amount  of  heat  lost  by  a  gas  in 
contact  with  its  enclosing  cold  surfaces 
depends,  first,  on  the  difference  in  tem- 
perature between  the  gas  and  the  cooling 
surfaces ;  secondly,  on  the  extent  of  sur- 
face exposed ;  and,  thirdly,  on  the  time 
of  exposure.  It  would  be  very  difficult 
to  make  an  accurate  numercial  compari- 
son between  the  engines,  but  all  to  be 
shown  is,  that  in  the  one  the  loss  of  heat 
must  be  less  than  in  the  other. 

To  compare  the  two  engines,  take 
equal  movements  of  the  pistons  from  a 
maximum  temperature  of  1,537°  Centi- 
grade. In  the  engine  working  without 
compression  this  temperature  is  attained 
at  the  middle  of  its  stroke,  when  the 
piston  has  moved  through  1  cubic  foot ; 
the  average  temperature,  while  it  moves 
to  the  end  of  its  stroke,  is  about  1,300° 
Centigrade. 

Now,  in  the  compression  engine  the 
maximum  temperature  is  attained  at  a 
point  when  the  piston  has  moved  through 


29 

0.39  cubic  foot:  suppose  it  to  move  to 
1.39  cubic  foot,  it  has  moved  through  1 
foot  in  the  same  time  as  the  first  engine. 
Then,  as  the  temperature  at  the  middle 
of  the  stroke  is  953°  (Fig.  4)  it  follows 
that  the  average  during  this  movement 
is  not  higher  than  1,000°  Centigrade,  but 
the  space  containing  the  heated  air  has 
increased  from  0.39  cubic  foot  to  1.39 
cubic  foot,  and  with  it  the  cooling  sur- 
face ;  whereas  the  space  containing  heat- 
ed air  in  the  first  engine  has,  during  the 
same  amount  of  movement,  increased 
from  1  cubic  foot  to  2  cubic  feet.  It 
follows  that  as  the  temperature  in  the 
compression  engine  is  1,000°  Centigrade 
during  the  same  time  as  the  temperature 
in  the  first  engine  is  1,300°  Centigrade? 
and  as  the  surface  in  it  for  cooling  is 
also  less,  the  amount  of  heat  lost  by  the 
air  must  be  less  in  the  portion  of  the 
stroke  under  consideration.  During  the 
portion  of  the  stroke  remaining,  0.61 
cubic  foot,  the  temperature  of  the  heated 
air  is  low,  falling  to  648°  Centigrade  at 
the  end  of  the  stroke ;  it  follows  that 


30 

very  small  comparative  loss  results.  Al- 
together the  loss  of  heat  by  the  com- 
pression engine  will  be  the  least. 

It  will  be  seen  from  Fig.  1  that  there 
is  a  further  cause  of  advantage.  While 
the  pressure  and  temperature  are  falling 
on  adiabatic  line  1,  the  work  done  by  1 
cubic  foot  of  air  on  expanding  to  the 
middle  of  the  stroke  at  a  temperature  of 
953°  Centigrade  is  7,888  foot-pounds, 
from  953°  Centigrade  to  G48°  is  3,202 
foot-pounds,  that  is,  7,888  foot-pounds 
of  work  are  performed  by  the  engine 
during  a  movement  of  the  piston  equal 
to  0.61,  while  in  the  engine  without  com- 
pression a  movement  of  1.00  cubic  foot 
only  does  5,731  foot-pounds. 

The  compression  engine  during  this 
portion  of  its  stroke  has  converted  the 
heat  entrusted  to  it  into  work  at  twice 
the  rate  of  the  other  engine.  This  is  a 
great  point.  Any  method  which  con- 
verts the  heat  into  work  with  the  utmost 
possible  rapidity,  by  reducing  the  time 
of  contact  between  the  hot  gases  and 
the  cylinder,  saves  heat  and  enables  the 


31 


theory  of  the  engine  to  be  more  nearly 
realized. 

Taking  all  circumstances  into  con- 
sideration, it  is  certainly  not  over  esti- 
mating the  relative  advantage  of  the  com- 
pression engine  to  say  that  it  will,  under 
practical  conditions  give,  for  a  certain 
amount  of  heat,  three  times  the  work  it 
is  possible  to  get  from  the  engine  using 
no  compression. 

It  will  not  be  necessary  to  discuss  the 
theory  of  type  2  in  respect  of  loss  of  heat 
to  the  sides  of  the  cylinder,  as  it  is  not 
much  used,  and  has  hitherto  failed  to 
yield  results  in  any  way  equal  to  type  3. 
It  will  be  seen,  however,  from  Fig.  3, 
that  the  conditions  are  not  so  favorable 
for  a  minimum  loss  of  heat  as  in  tvpe  3. 

The  temperature  from  the  moment  of 
admission  at  c,  to  the  point  of  cut-off 
at  e,  is  kept  constant  at  1,537°  Centi- 
grade, so  that  the  loss-  of  heat  must  be 
great,  both  the  surface  exposed  and  the 
mean  temperature  being  high.  It  is  the 
less  necessary  to  discuss  this  point  in 
the  slow  combustion  engine,  as  the  pos- 


32 

sibility  of  using  a  hot  cylinder  and  piston 
reduces  the  loss  by  attaining  a  tempera- 
ture not  far  removed  from  the  entering 
air. 

It  will  be  interesting  to  calculate  the 
amounts  of  gas  required  by  these  three 
types  under  the  supposed  conditions, 
and  for  this  purpose  an  analysis  of  Man- 
chester gas,  and  also  of  London  gas,  has 
been  used  as  the  basis  of  calculation. 

ANALYSIS    OF    MANCHESTER    COAL    GAS. 
BY    BUNSEN    AND    ROSCOE. 

Hydrogen 45.58 

March  gas 34.90 

Carbonic  oxide 6.64 

Olefiant  gas  or  ethylene 4 . 08 

Tetrylene 2.38 

Sulphuretted  hydrogen 0 . 29 

Nitrogen 2.46 

Carbonic  acid 3 . 67 


100. 00  volumes. 


Of  this  gas  1  Ib.  at  atmospheric 
pressure  and  17°  Centigrade  measures 
30  cubic  feet,  and  evolves  on  complete 
combustion  10,900  heat-units  Centigrade, 


33 

equivalent  to  15,146,640  foot-lbs.  1 
cubic  foot  of  this  gas  will  therefore 
evolve  on  complete  combustion  heat 

equivalent  to   -  —  =  504,888  foot- 

oU 

Ibs. 

To  obtain  an  idea  of  the  difference  in 
heating  power  of  the  different  gases, 
there  is  given  here  a  recent  analysis  of 
London  gas. 

ANALYSIS    OF    LONDON   COAL    GAS. 

(A.)  (B.) 

Hydrogen 50.05  51.24 

March  gas 32.87  35.28 

Carbonic  oxide 12.89          7.40 

defines 3.87          3.56 

Nitrogen —  2.24 

Carbonic  acid 0.32          0.38 

Taking  the  average  of  the  two  analyses, 
1  Ib.  weight  of  this  gas  at  atmospheric 
pressure. and  17°  Centigrade,  measures 
35.5  cubic  feet,  and  evolves  on  complete 
combustion  12,500  heat-units  Centigrade, 
equivalent  to  17,370,000  foot-lbs.,  1  cubic 
foot  of  this  gas  will  therefore  evolve,  on 


34 

complete  combustion,  heat  equivalent  to 
foot-lb, 


The  difference  between  the  heat  evolved 
by  these-  gases  is  but  small.  As  Glasgow 
coal  gas  is  of  a  high  illuminating  power, 
it  will  be  richer  in  olennes,  and  the 
heat  evolved  per  cubic  foot  will  be  some- 
what greater.  Taking  505,000  foot-lbs. 
as  the  amount  of  heat  evolved  by  1  cubic 
foot  of  coal  gas,  the  result  is  probably 
very  near  the  average  to  be  obtained 
from  the  coal  gas  of  most  towns.  The 
number  of  foot-lbs.  required  for  1  HP. 
for  one  hour  are  33,000x60=1,980,000. 
It  therefore  follows  that  if  the  whole 
heat  to  be  obtained  from  gas  were  con- 
verted into  mechanical  work,  1  HP.  for 

1,980,000 

one  hour  requires  —  =3.92  cubic 

505,000 

feet. 

Now,  taking  the  three  types  of  en- 
gines, the  amount  of  gas  required  by 
each  to  give  1  IHP.  per  hour  would  be 
as  follows  : 


35 


AMOUNT    OF    GAS    REQUIRED    BY    THREE    TYPES 
OF    ENGINE. 

3  92 
Typel.  Q1oi=18.3  cubic  ft.  per  HP.  perhr 


If  these  engines  be  worked  without 
loss  of  heat  through  the  sides  of  the 
cylinders,  but  the  expanding  g/ises  fall- 
ing in  temperature  only  through  doing 
work,  the  above  results  would  be  ob- 
tained. 

It  is  interesting  to  compare  the  con- 
sumption of  gas  by  the  engines  in  actual 
practice,  to  see  in  what  order  it  stands. 
Results  have  not  been  obtained  from  en- 
gines of  equal  volume  swept  through  by 
the  piston,  but  it  is  at  once  seen  that 
the  order  is  in  accordance  with  what  is 
required  by  theory. 


36 


AMOUNT    OF    GAS    CONSUMED     BY     THE     THREE 
TYPES  OF  ENGINE  HITHERTO  IN  PRACTICE. 

1.  Lenoir.  .95  cu.  ft.  per  indicated  HP.  per  hr. 
Hugon..85      " 

2.  Brayton.50      «        "  " 

3.  Otto 21       "        "  "  " 

For  the  Lenoir  and  Hugon  engines  the 
results  of  experiments  by  Mr.  Tresca,  of 
Paris,  have  been  taken,  as  stated  by 
Professor  Thurston,  corrected  for  an 
error  into  which  he  has  fallen.  He  states 
the  consumption  of  the  engine  to  be  32 
cubic  feet  per  IHP.  per  hour,  and  then 
goes  on  to  say  that  on  the  brake  4  HP. 
is  obtained,  while  8.6  is  indicated.  He 
has  neglected  to  deduct  from  the  gross 
indicated  power  in  the  cylinder,  the 
pump  resistance,  and  thus  calculates  the 
consumption  on  the  gross  indicated,  in- 
stead of  on  the  available  indicated 
power.  The  available  indicated  power 
is  not  more  than  5.2  HP.,  and  the  con- 
sumption is  not  less  than  50  cubic 
feet  per  IHP.  per  hour. 


37 

For  the  "Otto"  engine  have  been 
taken  the  figures  given  by  Mr.  F.  W. 
Crossley.  It  is  seen  that  the  results 
are  much  what  would  be  anticipated 
from  the  theory  already  developed.  The 
difference  between  types  1  and  3  is 
greater  than  theory  would  indicate  ;  but 
at  the  time  the  Lenoir  engine  was  in 
use,  the  imperfection  of  the  igniting  ar- 
rangements and  the  rapid  heating  of 
piston,  and  consequently  of  the  entering 
gases,  made  its  action  diverge  much 
more  widely  from  theory  than  in  the  case 
with  the  "  Otto."  The  latter  engine  not 
only  has  the  advantage  of  a  better 
theoretical  cycle,  but  the  arrangements 
are  of  a  nature  to  secure  a  greater  per- 
fection of  action,  and  consequently  a  still 
closer  approach  to  theory.  An  amount 
of  about  18  per  cent,  of  the  heat  used  by 
it  is  converted  into  work,  but  only  3.9 
per  cent,  by  the  Hugon  engine. 

In  types  1,  2  and  3,  which  have  been 
discussed,  it  has  been  assumed  that  in 
each  case  the  expansion  doing  work  was 


38 

carried  to  twice  the  volume  of  the  air 
before  compressing. 

Fig.  6  is  a  diagram  from  one  of  the 
author's  engines  which  belongs  to  type 
3.  It  will  be  observed  that  in  this  en- 
gine the  expansion  is  only  continued  un- 
til the  volume  of  the  hot  gases  becomes 
equal  to  the  volume  before  compression. 

Taking  the  amount  of  work  to  be  ob- 
tained from  a  cubic  foot  of  air  com- 
pressed to  40  Ibs.  above  the  atmosphere, 
and  then  heated  to  1,537°  Centigrade, 
expanding  as  the  piston  moves  to  its 
volume  before  compression,  and  then  ex- 
hausting, it  will  be  found  to  give  the 
following  results  : 

1  cubic  foot  of  air  (17°  Centi-  ] 
#rade  and  760  milimeters 
mercury)  at  constant  vol- 
ume requires  to  heat   it  i 
from  the  temperature  of  ^4,416  foot-lbs. 
compression  150°.  5  Centi- 
grade   to    1,537°    Centi- 
grade, heat  equivalent  to  j 

Maximum  pressure  in  Ibs.  \ 
per    square    inch    above  (•      220  Ibs. 
atmosphere ; 


39 


qoui  ejenbs 
jed-sq|  ui  sjai^dsoaiie  OAoqe  e 


. 


"  S 


0  . 


40 


Pressure  at  end  of  stroke  in  )        A(^  ^ 

r  <W    IDS. 

Ibs.  per  square  inch  .....  ) 
Mean  pressure  during  avail-  \ 
able  part  of    the  stroke  >        89.8 
above  atmosphere  .......  ) 

Temperature  at  the  end  of  }    953=  Centigrade. 
the  stroke  ..............  ) 

Work  done  on  the  piston.  .     7,888foot-lbs. 


Now  the  work  actually  given  by  1 
cubic  foot  of  combustible  mixture  in  the 
author's  engine,  as  will  be  seen  from  Fig. 
6,  is  6,851  foot-lbs.  The  full  lines  are 
the  diagram  lines  from  the  engine  ;  the 
dotted  lines  are  the  lines  of  compression 
and  expansion  without  loss  or  gain  of 
heat,  except  by  work  done  on  or  by 
the  air  under  similar  conditions  of 
temperature  and  compression.  It  will 
be  observed  that  the  compression  line 
and  the  dotted  line  are  very  close  to- 
gether ;  no  heat  seems  to  be  lost  to  the 
sides  of  the  cylinder  during  compres- 
sion ;  the  loss  of  heat  to  the  water-jacket 
is  balanced  by  the  gain  of  heat  from 


41 

the  piston,  which  must  necessarily  be 
much  hotter  than  the  cylinder  sides,  as 
it  only  loses  heat  by  contact  with  the 
cylinder  and  by  the  circulation  of  air 
in  the  trunk.  The  temperature  at- 
tained at  the  commencement  of  the  stroke 
is  in  both  esses  identical,  1,537°  Centi- 
grade ;  the  temperature  at  the  end  of 
the  stroke  without  loss  of  heat  is  953°; 
the  temperature  in  the  cylinder  at  the 
end  of  the  stroke  is  656°  Centigrade. 
The  diameter  of  the  cylinder  from  which 
this  diagram  was  taken  is  6  inches,  and 
ahe  length  of  stroke  12  inches.  This 
flppears  a  very  small  loss  of  heat  from  a 
tame  filling  the  cylinder,  considering  the 
surface  exposed  and  the  great  difference 
of  temperature  between  the  ignited  gases 
and  the  enclosing  walls.  Is  it  to  be  con- 
cluded, then,  that  the  loss  of  heat  to  the 
cylinder  during  the  time  of  the  forward 
stroke  is  only  953° -656°  =  297°  Centi- 
grade ?  On  this  assumption  the  duty  of 
the  engine  would  be — 


42 

and  the  consumption  of  gas  per  indicated 
HP.  per  hour  would  be  — 

3  92 

OT286=18-7  CUbi°  feet) 
but  the  consumption  is  22  cubic  feet  per 
indicated  HP.  per  hour,  so  that  there 
has  in  some  way  been  lost  much  more 
heat  than  is  to  be  accounted  for  by  the 
temperatures  as  determined  by  the  dia- 
gram. The  duty  of  the  engine  is  — 


The  duty  of  the  engine  expanding  to 
the  same  volume  as  the  mixed  gases  be- 

fore compression  is  — 

Gas  required 
per  IHP.  perhr. 

Cub.  ft. 

Duty  without  loss  of  heat  to 
/ 
sides  of  cylinder  .......... 

Duty  with  loss    of   heat    as 

shown  by  diagram 
Duty  as  determined  by  experi-  )  Q  ^      ^20 

ment  .....................  ) 

Now  the  number  of  cubic  feet  of  com- 
bustible mixture  required   to   produce  1 


HP.  for  one  hour  in  the  author'* 

1,980,000 
6,851 

The  amount  of  gas  in  the  engine  per 

22 

cubic  foot  of  mixture,  ^—  =0.0761  cubic 


foot,  or  =-Q  of  the  total  volume  of  gaseous 

JLO 

mixture  passed  into  the  engine.  If  only 
the  amount  of  gas  necessary  to  heat  the 
air  to  the  required  temperature  is  pres- 
ent, 1  cubic  foot  requires  0.0482  cubic 

foot  of  coal  gas,  or   about  —  of  its  vol- 

i£JL 

ume  ;  that  is,  although  to  heat  up  a  cubic 
foot  of  inflammable  mixture  from  150° 
Centigrade  to  1,537°'  only  0.0482  cubic 
foot  of  coal  gas  is  required,  yet  although 
there  is  present  0.0761  cubic  foot,  or  1.58 
time  the  amount  necessary,  the  tempera- 
ture does  not  rise  any  higher.  Why  is 
this? 

Before  going  into  the  question,  it  is 
better  to  determine  as  nearly  as  possible 
what  becomes  of  100  heat  units  used  bv 


44 

the  engine.  The  exhaust  being  dis- 
charged at  a  temperature  of  656°,  and 
the  temperature  of  the  air  before  com- 
pression being  assumed  at  17°,  it  fol- 
lows that  the  exhaust  from  1  cubic  foot 
carries  away  with  it  (656—17)  X  17.61  = 
11,253  foot-lbs. 

The  work  done  by  the  cubic  foot  of 
mixture  is  6,851  foot-lbs.,  and  the  equiva- 
lent in  foot-lbs.  of  the  gas  present  in  1 
cubic  foot  of  explosive  mixture  is  0.0761 
X  505,000=38,430  foot-lbs.  The  heat  is 
therefore  disposed  of  as  follows : 

Heat-units 
Foot-lbs.   percent. 
Work  done  by  1  cubic  foot  )    „  Q^       **  Qo 

>•     O,oOJL          l/.oo 

of  mixture ) 

Mechanical  equivalent  of  \ 

heat  discharged  with  the  ( 11,253      29 .£8 

exhaust ) 

Mechanical  equivalent  of  j 

heat  passing  through  sides  >•  20,326      52 . 89 

of  cylinder ) 

38,430    100.00 


This  investigation  is  only  approximate. 
The  determination,  with   anything   like 


45 

possible  physical  accuracy,  would  require 
an  examination  of  many  points  involving 
months  of  continuous  work.  It  is  the 
author's  intention  to  make  an  accurate 
research  into  the  phenomenon  attending 
the  use  of  the  gas  engine,  for  the  pur- 
pose of  obtaining  the  physical  constants 
necessary  to  calculate  exactly  the  con- 
sumption of  any  power,  size,  and  theory 
of  gas  engine,  such  as  it  may  be  possible 
to  construct  in  the  future.  For  the 
present,  however,  it  is  only  necessary  to 
discuss  the  principles  in  such  a  manner 
us  to  clearly  show  where  original  re- 
search is  required.  More  than  one-half 
of  the  total  heat  given  to  the  engine 
passes  through  the  sides  of  the  cylinder 
and  is  lost.  How  is  this  enormous  loss 
of  heat  sustained,  while  only  a  compara- 
tively small  fall  of  temperature  takes 
place  below  the  adiabatic  curve  ? 

This  leads  back  to  the  question  of 
the  gas  present  in  excess  of  the  amount 
necessary  to  raise  the  temperature  to 
1,537°  which  has  already  been  noticed. 
At  this  point  it  is  necessary  to  consider 


46 

the  gas   engine   as    something  different 
from  a  hot-air  engine. 

The  chemical  phenomena  attending 
combustion  now  require  consideration. 
If  2  volumes  of  hydrogen  be  mixed  with 
1  volume  of  oxygen  (the  proportions 
necessary  for  complete  combination  of 
both  gases  to  form  water),  and  be  ignited 
in  a  closed  vessel  in  such  a  manner  that 
the  maximum  pressure  may  be  measured, 
it  will  be  found  that  the  pressure  is  a 
much  lower  one  than  would  be  expected 
if  the  complete  combination  of  the  two 
gases  took  place  at  once,  and  the  whole 
heat  due  to  this  combination  were  de- 
veloped. That  this  is  not  due  to  loss  of 
heat  to  the  sides  of  the  vessel  has  been 
shown  by  Bunsen.  He  proved  that  the 
ratio  of  rise  in  pressure  is  exceedingly 
rapid  compared  to  the  rate  of  fall  of 
pressure.  The  time  taken  for  the  in- 
flammation of  the  whole  volume  of  mix- 
ture is  the  time  of  attainment  of  the 
maximum  pressure.  In  his  experiments 
he  used  only  a  very  small  tube,  which 
contained  a  volume  of  gaseous  mixture, 


47 

8.15  centimeters  long,  by  1.7  centimeter 
in  diameter,  and  the  entire  length  of 
this  column  was  traversed  by  the  electric 
spark,  in  order  that  the  inflammation  of 
the  whole  mass  in  the  tube  might  be  as 
nearly  instantaneous  as  possible.  In 
practice  he  succeeded  in  producing  a 
maximum  temperature  in  so  short  a  time 
as  j-yVo  part  of  a  second.  By  examining 
the  light  from  the  explosion  through  a 
revolving  disc  provided  with  radiating 
segments,  the  rate  of  revolution  of  the 
disc  being  known,  he  determined  the 
duration  of  light  within  the  tube,  and 
therefore  the  duration  of  a  temperature 
not  far  removed  from  the  maximum. 

The  duration  of  the  illumination  was 
found  to  be  -^of  a  second.  A  maximum 
pressure,  obtained  in  so  short  a  time, 
with  a  duration  so  relatively  long,  makes 
it  impossible  that  loss  of  heat  through 
the  sides  of  his  tube  could  have  affected 
his  experiments.  The  cause,  therefore, 
of  the  pressure  falling  so  far  short  of 
what  it  would  be  if  the  combination  took 
place  Sompletely.  is  simply  this,  that  the 


48 

temperature  is  so  high  that  complete  com- 
bustion is  impossible.  The  temperature, 
and  therefore  the  pressure  produced  by 
the  combination  of  any  gases,  is  limited 
by  the  dissociation  or  decomposition  of 
their  products  of  combustion. 

When  any  two  gases  combine,  say  (H) 
and  (O)  to  produce  water,  what  happens 
is  this.  The  temperature  rises  till  a 
point  is  reached,  when  any  further  rise 
would  decompose  the  water  which  is 
already  formed ;  and  if  the  gases  are 
kept  at  this  temperature,  no  further  com- 
bination will  take  place.  If  the  tempera- 
ture is  lowered,  further  combination 
takes  place  until  it  is  low  enough  to 
allow  of  the  existence  of  steam  without 
decomposition. 

The  temperature  at  which  steam  can 
exist  as  steam  without  its  partial  resolu- 
tion into  hydrogen  and  oxygen  gases  is 
not  a  high  one.  At  960°  to  1,000°  Centi- 
grade Deville  has  proved  that  it  com- 
mences to  decompose,  and  at  1,200° 
Centigrade,  considerable  decomposition 
takes  place,  the  amount  of  decomposition 


49 

increasing  as  the  temperature  rises  :  for 
each  temperature  there  is  a  proportion 
of  steam  to  free  gases,  which  is  constant, 
and  does  not  change  till  the  temperature 
changes.  The  same  law  holds  true  for 
carbon  dioxide ;  at  high  temperatures  it 
decomposes  into  carbonic  oxide  and  free 
oxygen. 

Bunsen  attempted  to  determine  the 
temperature  attained  on  the  explosion  of 
a  mixture  of  hydrogen  and  oxygen,  a 
pure  electrolytic  mixture.  He  found 
that  the  maximum  pressure  attained  by 
such  a  mixture  is  10  atmospheres,  the 
temperature  before  ignition  being  5° 
Centigrade.  From  this  he  calculated 
the  temperature  produced,  but  in  doing 
so,  as  Berth elot  afterwards  pointed  out, 
he  neglected  the  fact  that  when  these 
gases  combine,  3  volumes  of  the  gases 
form  2  volumes  of  steam  gas,  and  con- 
sequently if  complete  combination  is 
assumed,  and  it  be  supposed  that  the 
pressure  is  produced  by  steam  only,  the 
volume,  before  ignition,  must  be  calcu- 
lated at  two-thirds  of  that  taken  by  the 


50 

mixed  gases.  But  as  it  is  known  that 
combination  is  incomplete,  at  the  lowest 
assignable  temperature  of  the  combus- 
tion, and  it  is  not  possible  to  tell  the 
amount  of  combination  at  a  given  press- 
ure without  knowing  the  temperature, 
this  cannot  be  assumed. 

As  in  determining  temperature  by  an 
air  thermometer  it  is  necessary  that  the 
amount  of  air  in  the  thermometer  should 
be  constant  at  the  different  temperatures, 
it  is  evident  that  the  temperature  of  an 
explosion  cannot  be  known  from  the  in- 
crease in  pressure  unless  the  chemical 
changes  taking  place  do  not  alter  the 
volume  of  gases  under  observation. 

In  calculating  the  temperatures  at 
tained  in  the  author's  engine,  this  fact 
has  been  kept  in  view.  The  capacity  ol 
the  space  at  the  end  of  the  cylinder  was 
carefully  taken  by  filling  with  water  and 
weighing,  the  water.  As  the  proportion 
of  the  combining  gases  to  the  excess  of 
oxygen  or  free  nitrogen  is  very  small, 
only  one-thirteenth  of  the  whole  volume 
used  being  combustible  gas,  the  space 


51 

may  be  considered  as  simply  filled  with 
heated  air,  and  the  contraction  caused  by 
the  formation  of  H^O  and  CO,  neglected, 
especially  as  an  increase  in  volume  fol- 
lows the  combination  of  the  olefines  with 
oxygen.  2  volumes  of  H  combine  with 
1  volume  of  O,  forming  2  volumes  of 
steam.  2  volumes  of  marsh  gas  (CH4) 
require  for  complete  combustion  4  vol- 
umes of  O,  and  form  4  volumes  of  H20 
and  2  volumes  of  CO.,.  2  volumes  of 
carbonic  oxide  (CO)  unite  with  1  volume 
of  O,  forming  2  volumes  of  CO2.  If  the 
olefines  in  coal  gas  be  taken  as  of  an 
average  composition  of  C3H6,  then  2 
volumes  require  for  complete  combustion 
9  volumes  of  oxygen,  forming  6  volumes 
of  H2O  and  6  volumes  of  CO2. 

Now  taking  the  composition  of  coal 
gas  as  below  the  noted  amounts  of  oxy- 
gen are  required  for  combustion,  and 
the  given  volumes  of  the  products  are 
formed — 


52 


vols.  vols.        vols. 

H=50  requires  25  O=50  H8O  produced. 

CH4=33        "       66  O=99  CO4&H2O  " 

CO=13        "      6.5  O=13  CO2 

C3H6  =  4        "       IS  O=24  CO2&H2O  " 

100  +        115.5=225.5  gives  186  vols. 

The  amount  of  contraction  due  to  com- 
plete combustion  of  this  coal  gas  is  small 
even  when  burning  with  pure  oxygen, 
225  volumes  of  the  mixed  gases  becom- 
ing 186  volumes  after  combustion.  When 
diluted  with  nitrogen  the  proportion  of 
contraction  is  less  and  introduces  no 
serious  error.  With  a  mixture  of  1 
volume  of  gas  to  12  volumes  of  air,  125 
volumes  of  the  mixture  before  combina- 
tion become  122  volumes  when  complete- 
ly combined,  at  the  original  temperature, 
assuming  the  water  to  remain  gaseous. 
If  the  curve  of  the  dissociation  of  water 
and  carbonic  dioxide  were  known,  it 
would  be  possible  to  show  on  the  indica- 
tor diagram  the  reserve  of  heat  available 
at  each  point  of  the  fall. 

What   the   engineer   requires   of    the 


53 

scientific  chemist  is  a  curve  of  the  disso- 
ciation of  water  and  carbonic  acid,  at 
temperatures  ranging  from  the  maximum 
produced  by  combustion  down  to  the 
point  at  which  it  may  be  safely  assumed 
that  complete  combination  is  possible. 

In  Fig.  6  the  dotted  line  shows  a  fall 
of  temperature,  by  hot  air  doing  work 
without  loss  of  heat  through  the  cylinder, 
and  the  black  line  shows  the  actual  fall 
of  temperature  in  the  author's  engine, 
with  ]oss  of  heat  through  the  sides  of  the 
cylinder.  It  is  evident  then  that  the 
cause  of  so  near  an  apparent  approach  to 
theory  is,  that  at  the  maximum  tempera- 
ture, complete  combination  of  gases  with 
oxygen  is  impossible,  and  cannot  take 
place  until  the  temperature  falls.  As 
the  temperature  falls  the  gases  further 
combine,  until  a  temperature  is  reached 
at  which  combination  is  complete. 

The  loss  of  heat  through  the  sides  of 
the  cylinder  is  therefore  much  greater 
than  would  appear  from  the  diagram.  In 
calculating  the  efficiency  of  the  gas  en- 
gine, all  previous  observers  have  assumed 


54 

that  the  loss  of  heat  to  the  cylinder  is  to 
be  obtained  from  the  comparison  on  the 
indicator  diagram  of  the  actual  expan- 
sion-line with  an  adiabatic  line  from  the 
same  maximum  temperature  and  press- 
ure. So  far  as  the  author  is  aware, 
Professor  Riicker,  of  Leeds,  was  the 
first  to  point  out  the  necessity  of  taking 
into  account  the  phenomena  of  dissocia- 
tion in  making  such  comparisons.  Ac- 
cordingly, all  previous  estimates  of  effi- 
ciency, based  on  the  indicator  diagrani, 
are  much  too  high. 

The  gas  engine,  then,  differs  from  the 
hot-air  engine,  using  air  heated  in  the 
manner  assumed  in  the  first  part  of  this 
paper,  in  this,  that  the  temperature  is 
sustained,  notwithstanding  the  enormous 
flow  of  heat  through  the  sides  of  the 
cylinder,  by  the  continuous  combination 
of  the  dissociated  gases. 

Figs.  7  and  8,  have  been  taken  from 
the  "Journal  of  the  Franklin  Institute." 
They  are  Lenoir  engine  diagrams,  and  in 
them  the  same  phenomena  are  apparent ; 
although  running  at  a  very  slow  speed, 


55 

the  pressure  is  most  perfectly  sustained, 
the  dotted  lines  showing  the  adiabatic, 
and  the  full  lines  the  actual  diagram. 
The  author  of  the  paper  in  which  they 
occur,  gives  the  probable  maximum  tem- 

Fig.7. 


LENOIR    ENGINE. 

Diagram  at  50  revolutions,  cylinder  8^  inches 
diameter,  16^  inches  stroke. 


LENOIR   ENGINE. 
Diagram  at  45  revolutions,  1  inch =32  Ibs. 


56 


perature  attained  at  about  1,356°  Centi- 
grade, and  he  says,  "The  dotted  line 
represents  the  theoretical  curve  of  ex- 
pansion, taking  into  account  the  loss  of 
heat  and  consequent  fall  of  pressure,  due 
to  the  work  done  (which  is  the  proper 
theoretical  curve  for  an  indicated  dia- 
gram). The  temperature  at  the  end  of 
the  stroke,  indicated  by  this  line,  would 
be  2,156°  Fahrenheit  (1,180°  Centigrade). 
The  final  temperature  shown  by  the  dia- 
gram, supposing  there  be  no  leakage,  is 
1,438°  Fahrenheit  (781°  Centigrade),  and 
the  difference  718°  Fahrenheit  (399° 
Centigrade),  is  the  quantity  of  heat  ab- 
sorbed by  the  water-jacket  by  which  the 
cylinder  is  surrounded." 

"  It  will  be  observed  that  the  explo- 
sion takes  place  so  late  in  the  stroke  that 
there  is  a  considerable  available  pressure 
at  the  end  of  the  stroke,  which  of  course 
is  not  utilized." 

Now  if  the  Lenoir  engine  had  only 
lost  this  amount  of  heat  through  the 
sides  of  the  cylinder  it  would  have  been 
very  economical,  and  would  have  ap- 


57 

preached  the  theoretic  consumption 
mentioned  in  the  earlier  part  of  this 
paper;  but  the  causes  of  loss  are  so 
great  that  it  never  did  come  anything 
near  this  figure,  and  an  erro"r  is  intro- 
duced through  neglecting  the  effects  of 
dissociation. 

Interesting  information,  however,  is  to 
be  obtained  from  these  diagrams  as  to 
the  proportion  of  gas  and  air  in  the  mix- 
ture used  by  the  Lenoir  engine.  When 
these  diagrams  were  taken  the  maximum 
temperature  after  ignition  was  1,356° 
Centigrade  ;  now  in  the  author's  present 
engine  the  maximum  temperature  is 
1,537°;  it  follows  that  Lenoir  used  a 
more  diluted  mixture  as  the  temperature 
after  ignition  was  lower.  The  engine 
giving  this  diagram  could  not  have  been 
using  an  ignitable  mixture  containing 
more  gas  than  one-fourteenth  of  its  vol- 
ume—a mixture  which  the  author  finds 
to  be  easily  ignited  at  ordinary  atmos- 
pheric pressure.  The  statement  is  often 
made  that  such  a  mixture  will  not  ex- 
plode except  it  be  first  compressed  ;  this 


58 

is  incorrect,  it  is  possible  to  ignite  even 
a  weaker  mixture  without  compression. 
Coquillon  has  determined  the  limits  be- 
tween which  a  mixture  of  marsh  gas 
(CH4)  and  .air  can  be  exploded.  Mixtures 
of  marsh  gas  and  air  in  different  propor- 
tions were  introduced  into  a  eudiometer 
and  fired  by  the  electric  spark,  with  the 
following  results : 

Marsh  gas  1  volume,  air  5  volumes. 
The  spark  is  without  effect.  Marsh  gas 
1  volume,  air  6  volumes.  Explosion  only 
occurs- in  a  succession  of  shocks.  This 
is  the  first  limit  of  possible  explosion ; 
the  marsh  gas  is  in  excess.  Marsh  gas 
1  volume  and  7,  8  and  9  volumes  of  air 
give  a  sharp  explosion.  With  12,  13, 14, 
15  volumes  of  air  for  1  volume  of  marsh  gas 
the  explosion  occurs,  but  grows  gr^dual- 
ly  weaker.  With  16  volumes  of  air  the 
effect  is  reduced  to  a  series  of  slight  in- 
termittent commotions.  This  is  the 
second  limit ;  the  air  is  in  excess. 

In  Fig.  8,  ignitions  will  be  observed 
very  late  in  the  stroke ;  these  misses 
were  caused  by  the  points  between  which 


59 

the  electric  spark  is  discharged  getting 
wet  and  thus  preventing  the  passage  of 
the  spark  at  the  proper  time.  From 
these  diagrams,  the  time,  from  the  begin- 
ning of  rise  in  pressure  to  the  attainment 
of  maximum  pressure,  is  found  to  be 
from  one  twenty-seventh  to  one-thirtieth 
of  a  second ;  when  the  ignitions  are  late 
it  takes  longer,  one-twentieth  of  a  second 
being  required  ;  that  is,  the  flame  has 
spread  completely  through  the  mass  in 
one-twentieth  part  of  a  second. 

Now  in  the  author's  engine,  calculating 
from  the  moment  when  the  ignition  port 
is  opening  to  the  flame,  to  the  moment 
of  maximum  pressure  as  found  from  the 
diagrams,  it  has  been  ascertained  that 
the  time  occupied  is  an  average  of  one 
twenty-fifth  of  a  second,  a  time  nearly 
identical  with  that  found  for  the  Lenoir 
engine. 

If  it  be  admitted  that  the  flame  has 
spread  completely  through  the  mass 
when  the  maximum  pressure  is  attained 
in  the  Lenoir  engine,  it  cannot  be  sup- 
posed that  it  has  not  spread  in  like  man- 


60 

ner  throughout  the  mass  of  ignitable 
mixture  in  the  modern  compression  en- 
gine. Maximum  pressure  is  the  only 
outward  indication  of  complete  inflamma- 
tion ;  by  complete  inflammation  is  not 
meant  the  thorough  chemical  combina- 
tion of  the  active  gases  present,  but  the 
spread  of  the  flame  through  the  entire 
mass.  That  when  maximum  pressure 
has  been  reached  complete  inflammation 
has  also  been  attained  has  hitherto  been 
considered  self-evident.  It  is  only  lately 
that  the  theory  has  been  advanced  by 
Mr.  Otto  that  in  the  modern  compression 
engine  attaining  maximum  pressure  at 
the  beginning  of  the  stroke,  the  flame  has 
not  spread  throughout  the  mass  of  the 
ignitable  mixture  in  the  cylinder;  but  that 
as  the  piston  moves  forward  the  pressure 
js  sustained  by  the  gradual  spread  of  the 
flame.  This  supposed  phenomenon  has 
been  erroneously  called  slow  combustion ; 
if  it  has  any  existence  it  should  be  called 
slow  inflammation.  It  has  a  real  existence 
in  the  Otto  engine  only  when  it  is  working 
badly  ;  but  even  then  maximum  temper- 


61 

ature  is  attained,  and  very  distinctly 
marks  the  point  of  completed  inflamma- 
tion. 

The  time  taken  to  attain  maximum 
pressure  is  longer  in  a  large  engine  than 
in  a  small  one,  because  the  distance 
through  which  the  flame  has  to  travel  is 
greater.  During  the  investigation  al- 
ready referred  to,  Professor  Bunsen 
determined  the  celerity  of  the  propaga- 
tion of  ignition  through  a  pure  explosive 
mixture  of  hydrogen  and  oxygen  in  the 
following  manner  :  the  explosive  mixture 
was  allowed  to  burn  from  a  fine  orifice  of 
known  diameter,  and  the  current  of  the 
rate  of  the  gaseous  mixture  was  carefully 
regulated  by  diminishing  the  pressure^ 
to  the  point  at  which  the  flame  passed 
back  through  the  orifice  and  ignited  the 
gases  below  it.  This  passing  back  of 
the  flame  occurs  when  the  velocity  with 
which  the  gaseous  mixture  issues  from 
the  orifice  is  inappreciably  less  than  the 
velocity  with  which  the  inflammation  of 
the  upper  layers  of  burning  gas  is  propa- 
gated to  the  lower  and  unignited  layers. 


62 

The  rate  of  the  propagation  of  the 
ignition  in  pure  hydrogen  was  found  to 
be  34  meters  per  second.  In  a  maximum 
explosive  mixture  of  carbonic  oxide  and 
oxygen  it  was  not  quite  1  meter  per 
second. 

Mr.  Mallard  has  determined  the  rapid- 
ity of  the  propagation  of  inflammation 
through  mixtures  of  coal  gas  and  air  by 
this  method,  and  found  that  the  maxi- 
mum rate  of  propagation  was  attained 
with  a  mixture  of  1  volume  of  coal  gas 
with  5  volumes  of  air,  and  it  is  1.01  meter 
per  second.  One  volume  of  coal  gas  with 
6J  volumes  of  air  gave  a  rate  of  0.285 
meter,  or  11  inches  per  second. 

This  is  the  rate  of  ignition,  it  must  be 
remembered,  at  constant  pressure  ;  in  a 
closed  tube  fired  at  one  end  it  would  ig- 
nite with  much  greater  rapidity.  In  a 
closed  space  the  conditions  of  inflamma- 
tion are  quite  different.  The  ignited 
portion  instantly  expands,  compressing 
the  portion  still  remaining,  and  thus  car- 
ries the  flame  further  into  the  mass,  so 
that  to  the  rate  of  ignition  at  constant 


63 

pressure  is  added  the  projection  of  the 
flame  into  the  mass  by  its  expansion.  To 
determine  from  the  rate  of  ignition  at 
constant  pressure  the  time  necessary  to 
completely  inflame  a  given  volume  of 
mixture  at  constant  volume  is  a  very 
complicated  problem,  which  it  is  proba- 
ble can  only  be  solved  experimentally. 

The  author  has  found  it  possible  to 
ignite  a  whole  mass  in  any  given  time 
between  the  limits  of  one-tenth  and  one- 
hundredth  part  of  a  second,  by  so  arrang- 
ing the  plan  of  ignition  that  a  small  vol- 
ume of  gaseous  mixture  is  first  ignited, 
expanding  and  projecting  a  flame  through 
a  passage  into  the  mass  of  inflammable 
mixture,  and  thus  adding  to  the  rate  of 
ignition  the  mechanical  disturbance  pro- 
duced by  the  entering  flame.  He  has 
succeeded  by  this  means  in  producing 
maximum  pressure  in  one-hundredth 
part  of  a  second  in  a  space  containing 
200  cubic  inches.  This  rate  of  ignition 
is  too  rapid,  and  would  not  give  the  en- 
gine time  to  take  up  the  slack  in  bearings, 
connecting  rods,  &c.  But  by  firing  a 


64 

mixture  with  varying  amounts  of  mechan- 
ical disturbance  almost  any  time  of  igni- 
tion can  be  obtained  between  -^--^  and  -^ 
of  a  second.  It  does  not  matter  whether 
the  mixture  used  is  rich  or  weak  in  gas  ; 
the  rich  mixture  can  be  fired  slowly  and 
the  weak  one  rapidly,  just  as  may  be  re- 
quired. The  rate  of  ignition  of  the 
strongest  possible  mixture  is  so  slow  that 
the  time  of  attaining  complete  inflamma- 
tion depends  on  the  amount  of  mechani- 
cal disturbance  permitted. 

Fig.  9,  a  diagram  from  an  Otto  engine, 
shows  what  happens  in  a  compression 
engine  of  type  3  when  the  ignition  comes 
late  and  the  movement  of  the  piston 
overruns  the  rate  of  the  spread  of  the 
flame.  It  is  then  seen  that  the  maximum 
pressure  is  not  attained  until  far  on  in 
the  stroke,  and  as  a  consequence  great 
loss  of  power  results,  the  pressure  at- 
taining its  maximum  when  it  is  time  for 
the  exhaust  valve  to  open.  This  may 
happen  from  several  causes,  a  too  diluted 
mixture,  or  too  little  mechanical  disturb- 
ance by  the  entering  flame;  or  the  igni- 


65 


66 

tion  may  be  missed  until  the  pressure 
begins  to  fall  by  the  forward  movement 
on  the  piston,  when  the  rate  of  inflamma- 
tion begins  to  come  more  nearly  to  Mal- 
lard's number  of  11  inches  per  second. 
This  slow  combustion,  or  rather  slow  in- 
flammation, is  to  be  avoided  in  the  gas 
engine.  Every  effort  should  be  made  to 
secure  complete  inflammation  as  soon 
after  ignition  as  is  practicable.  The  lines 
in  the  diagram  show  this  very  clearly  ; 
the  normal  lines  are  those  in  which  the  rise 
is  almost  straight  up  from  the  point  of 
the  beginning  of  the  ignition  ;  they  are 
marked  a  and  b  ;  the  line  c,  although  com- 
mencing from  the  beginning  of  the  stroke, 
does  not  record  the  maximum  pressure 
till  the  piston  has  moved  forward  one- 
third  of  its  stroke,  while  the  line  d  does 
not  depart  from  the  compression  line 
until  one-tenth  of  the  forward  movement, 
and  does  not  attain  its  maximum  till  near 
the  end  of  the  stroke.  In  the  last  case 
the  ignition  has  been  missed  until  the  pis- 
ton is  in  rapid  motion,  and  consequently 
the  flame  is  at  first  unable  to  overtake  it. 


67 

The  rate  of  inflammation  at  constant 
pressure  has  been  determined  only  for 
atmospheric  pressure ;  were  it  known  for 
higher  pressures  it  would  be  possible  to 
calculate  exactly  the  piston  speed  which 
would  prevent  any  rise  in  pressure  at  all. 

Fig/ 10  was  taken  by  the  author  from 
the  motor  cylinder  of  an  American  Bray- 
ton  engine  of  type  2.  It  shows  how  the 
pressure  is  sustained  as  the  ignited  gases 
enter  the  motor  cylinder  in  flame.  This 
is  the  true  slow  inflammation  engine  ;  in 
it  the  pressure  after  ignition  is  not  al- 
lowed to  rise,  but  only  increase  of  volume 
takes  place ;  at  about  the  middle  of  the 
stroke  the  supply  of  flame  is  cut  off  and 
the  piston  moves  on,  and  the  heated  gases 
expand  doing  work. 

Fig.  11  is  the  compression  pump  dia- 
gram, which  must  be  deducted  before 
getting  the  available  indicated  power. 
The  motor-piston  was  of  the  same  area 
as  the  pump,  but  had  double  the  length 
of  stroke.  This  type  of  engine  is  not  a 
good  one  for  a  cold  cylinder,  the  loss  of 
heat  through  the  cylinder  being  much 


68 


more  than  in  type  3  ;   but,  as  it  has  been 
before  said,  the  possibility  of  using  the 


w 
ft 


tf 

g 

O 


§ 

o 


g 


2 

-< 


theory  in  the  future  with  a  hot  piston  and 
cylinder  renders  reference  to  this  engine 


69 

interesting.     Slow  inflammation  is  a  mis- 
take if  applied  to  engines  of  types  1  and 


3  with  cold  cylinders ;  in  type  1,  if  the 
piston  were  moving  rapidly  enough,  the 
inflammation  could  be  so  slow  that  with 


70 

a  perfectly  sustained  temperature  no 
power  at  all  could  be  obtained.  That  is, 
the  air  would  simply  expand  in  volume 
without  rising  in  pressure  above  the 
atmosphere,  and  even  without  loss  of 
heat  to  the  sides  of  the  cylinder  the 
whole  heat  would  be  uselessly  discharged. 
In  type  3  the  perfection  of  slow  com- 
bustion would  be  attained  when  the  flame 
spread  just  as  rapidly  as  the  piston  moves 
forward,  and  the  pressure  was  never 
raised  above  that  due  to  compression. 
The  pressure  diagram  would  then  give 
the  ideal  results  of  "  gradual  expansion 
of  gases"  and  a  "perfectly  sustained 
pressure."  But  this  is  just  the  condition 
of  greatest  loss  of  heat ;  sustained  press- 
ure means  sustained,  indeed  increasing 
temperature,  and  the  object  to  be  attained 
in  a  good  gas  engine  is  to  produce  the 
most  rapid  possible  fall  of  temperature 
due  to  work  performed,  to  keep  the  mean 
temperature  as  low  as  possible,  and  it  is 
only  so  far  as  this  is  successfully  done 
that  economy  is  possible.  Slow  inflam- 
mation causes  loss  of  heat  and  power; 


71 

rapid  inflammation  reduces  the  loss  to  a 
minimum  while  attaining  the  maximum 
possible  power. 

One  more  engine  may  be  noticed  ;  its 
diagram  is  given  at  Fig.  12.  In  action  it 
comes  under  type  1,  but  uses  a  very 
large  amount  of  expansion,  and  is  further 
complicated  by  cooling.  It  is  the  well- 
known  Otto  and  Langen  engine  of  the 
free  piston  type  ;  in  it  gas  and  air  are 
taken  in,  for  a  portion  of  the  stroke  at 
atmospheric  pressure  and  then  ignited 
while  the  piston  remains  at  rest  until  the 
pressure  sets  it  in  motion;  the  piston  is  free 
to  move  apart  from  the  shaft  altogether, 
and  on  the  up- stroke  it  does  no  work. 

From  f  to  a  air  and  gas  are  taken 
into  the  cylinder.  At  a  the  mixture  is 
ignited  and  the  .piston  moves  to  c  with 
considerable  velocity  when  the  pressure 
has  fallen  to  the  atmosphere.  From  c 
to  e  it  continues  to  move  with  continually 
diminishing  velocity,  until  at  e  it  comes 
to  rest  and  then  returns  doing  work,  the 
work  being  equal  to  the  diagram  d  g  e 
added,  to  the  weight  of  the  piston  and 


lOOr 


60 


72 


Fig.12, 


10     20     30     40     50     60 


70     80 


OTTO    AND    LANGEN    ENGINE    (FREE   PISTON). 
Percentage  of  stroke. 


73 

rack  through  the  stroke.  It  will  at  once 
be  seen  that  as  the  gases  only  do  work 
on  the  piston  from  a  to  c,  and  this  work 
is  absorbed  in  giving  a  certain  velocity 
to  the  piston,  and  from  c  to  e  the  velocity 
of  the  piston  is  being  gradually  checked 
by  doing  work  on  air,  assuming  the  pis- 
ton to  have  no  weight,  the  area  of  the 
portion  of  the  diagram  a  c  b  must  be 
equal  to  the  part  c  e  d. 

It  is  evident  that  the  lines  in  the  dia- 
gram are  incorrect ;  the  explosion  cannot 
fall  nearly  so  rapidly  as  shown  ;  c  should 
be  much  nearer  e.  The  oscillations  of 
the  indicator  have  been  so  great  that  ac- 
curacy is  impossible.  The  fall  of  the 
line  d  g  below  d  e  is  caused  by  the  cool- 
ing of  the  gases  on  the  return  strokte. 
In  this  engine  the  advantage  consists 
more  in  the  large  amount  of  expansion 
than  the  velocity  of  the  forward  move- 
ment of  the  piston. 

The  diagram  has  been  taken  from  a 
paper  by  Mr.  F.  W.  Crossley  ;  with  ref- 
erence to  it  he  says : 

"  The  very  sudden  and  extreme  rise  in 


74 

pressure  at  the  moment  of  explosion  is 
due  simply  to  the  expansion  of  the  gases 
under  the  temperature  of  the  flame.  If 
this  temperature  be  taken  at  5,000° 
Fahrenheit,  and  divided  by  520  for  the 
rate  of  expansion  from  an  initial  tempera- 
ture of  about  60°,  it  gives  an  expansion 
of  about  10  times  ;  and  as  the  gas  com- 
pound occupied  one-eleventh  of  the 
cylinder  at  the  moment  of  ignition,  if  it 
expands  ten  times  it  gives  very  nearly 
the  stroke  actually  takc?n  by  the  piston. 
The  5,000°  is  an  assumption  only,  but 
seems  to  be  confirmed  by  the  amount  of 
expansion  which  follows  it.  After  the 
explosion  the  temperature  falls  almost 
instantaneously,  as  shown  by  the  sudden 
drop  of  pressure  in  the  diagram." 

In  the  author's  opinion  Mr.  Crossley 
has  completely  misinterpreted  his  dia- 
gram. Taking  the  temperature  before 
ignition  at  60°  Fahrenheit,  and  the  maxi- 
mum pressure  shown  on  the  diagram  as 
100  Ibs.  absolute,  it  follows  that  the 
maximum  temperature  is  not  greater 
than  2,900°  Fahrenheit  (1,590°  Centi- 


•  75 

grade).  It  is  difficult  to  see  how  5,000° 
Fahrenheit  can  be  assumed.  The  ex- 
pansion of  the  gases  by  the  extreme 
movement  of  the  piston  following  igni- 
tion has  no  necessary  relation  to  the 
temperature  of  the  explosion ;  but  it  is 
determined  wholly  by  the  work  done  on 
the  piston  by  the  explosion  between  the 
maximum  and  atmospheric  pressures. 
Whenever  the  gases  in  the  cylinder  fall 
to  the  pressure  of  the  atmosphere, 
which  happens  according  to  the  diagram 
at  about  0.35  of  the  stroke,  the  piston  is 
doing  work  on  air,  and  the  mean  press- 
ure below  the  atmosphere  from  c  to  e  is 
the  exact  measure  of  the  work  previously 
done  on  the  piston  by  the  explosion, 
which  has  been  expended  in  giving  the 
piston  velocity.  This  energy  of  motion 
is  now  being  expended  by  compressing 
the  atmosphere.  Taking  into  consider- 
ation the  weight  of  the  piston  and  fric- 
tion of  the  rings,  rack  and  clutch,  it  is 
certain  that  the  area  of  the  part  of  the 
diagram  a  b  c  must  be  considerably 
greater  than  c  e  d\  in  the  diagram  it  ap- 


76 

pears  much  less.  It  should  be  greater  by 
the  amount  of  work  expended  in  giving  the 
piston  energy  of  position,  and  the  amount 
lost  by  friction  on  the  up-stroke. 

As  a  means  of  showing  the  nature 
of  the  explosion  this  diagram  is  mislead- 
ing ;  it  is  certain  that  the  maximum  press- 
ure was  less,  and  that  the  fall  of  press- 
ure is  nothing  like  so  rapid  as  it  there 
appears.  Comparing  Fig.  12  with  Figs. 
7  and  8  the  difference  in  appearance  is 
so  striking  that  it  looks  as  if  in  one  case 
the  fall  in  pressure  was  instantaneous 
and  in  the  other  gradual ;  this  would  be 
remarkable,  considering  that  the  maxi- 
mum temperatures  are  very  similar.  If 
the  lines  in  Fig.  12  be  corrected  and 
drawn  with  the  same  relation  of  scale 
between  pressures  and  strokes,  it  will  be. 
found  to  be  very  similar  in  appearance 
to  Figs.  7  and  8,  so  far  as  rate  of  fall  is 
concerned.  Indeed  the  advantage  claimed 
for  this  engine  is  a  movement  of  piston 
so  rapid  that  its  expansion  is  complete 
before  much  heat  is  lost  to  the  sides  of 
the  cylinder,  which  is  inconsistent  with  a 


77 

fall  of  pressure  more  rapid  than  in  the 
Lenoir  engine. 

To  go  completely  into  the  points  of 
originality  in  these  engines  would  require 
a  paper  on  the  "  History  of  the  Gas  En- 
gine ; "  but  it  may  be  well  to  state  the 
name  of  the  first  to  propose  each  type : 

Year. 

Type  1.  Explosion  acting  on  piston  con- 
nected to  crank. .  .W.  L.Wright  1833 
Explosion  acting  on  free  piston, 

Barsanti  &  Matteuci  1857 
Type  2.  Compression  after  ignition  but  at 

constant  presssure.  C.  W.  Siemen  s  1 860 
Compression  with  increase  in  vol- 
ume  F.  Millon  1861 

Type  3.   Compression    with    incrro.se    in 

pressure - F.  Millon  186L 

After  ignition   but    at    constant 
volume 

So  far  as  the  author  has  been  able  to 
ascertain,  these  are  the  names  of  the  first 
to  propose  distinctly  each  of  the  three 
types  of  gas  engine. 

From  the  considerations  advanced  in 
the  course  of  this  paper,  it  will  be  seen 
that  the  cause  of  the  comparative  ef- 
ficiency of  the  modern  type  of  gas  en- 


78 

gines  over  the  old  Lenoir  and  Hugon  is 
to  be  summed  up  in  one  word,  "  com- 
pression." Without  compression  before 
ignition  an  engine  cannot  be  produced 
giving  power  economically  and  with 
small  bulk.  The  mixture  used  may  be 
diluted,  air  may  be  introduced  in  front 
of  gas  and  air,  or  an  elaborate  system  of 
stratification  may  be  adopted,  but  with- 
out compression  no  good  effect  will  be 
produced. 

The  proportion  of  gas  to  air  is  the 
same  in  the  modern  gas  engine  as  was 
formerly  used  in  the  Lenoir,  the  time 
taken  to  ignite  the  mixture  is  the  same, 
the  only  difference  is  compression.  The 
combustion,  or  rather  the  rate  of  inflam- 
mation, is  indeed  quicker  in  the  modern 
engine  because  the  volume  of  mixture 
used  at  each  stroke  is  greater,  and  yet 
the  time  taken  to  completely  inflame  the 
mixture  is  no  more  than  in  the  old  type. 
The  cause  of  the  sustained  pressure 
shown  by  the  diagrams  is  not  slow  in- 
flammation (or  slow  combustion  as  it  has 
been  called),  but  the  dissociation  of  the 


products  of  combustion,  and 
ual  combination  as  the  temperature  falls, 
and  combination  becomes  possible.  This 
takes  place  in  any  gas  engine,  whether 
using  a  dilute  mixture  or  not,  whether 
using  pressure  before  ignition  or  not, 
and  indeed  it  takes  place  to  a  greater  ex- 
sent  in  a  strong  explosive  mixture  than 
in  a  weak  one. 

The  modern  gas  engine  does  not  use 
slow  inflammation  (or  slow  combustion  if 
the  term  be  preferred),  but  when  work- 
ing as  it  is  intended  to  do,  completely  in- 
flames its  gaseous  mixture  under  com- 
pression at  the  beginning  of  the  stroke. 
By  complete  inflammation  is  meant  com- 
plete spread  of  the  flame  throughout  the 
mass,  not  complete  burning  or  combus- 
tion. If  by  some  fault  in  the  engine  or 
igniting  arrangement  the  inflammation  is 
a  gradual  one,  then  the  maximum  press- 
ure is  attained  at  the  wrong  end  of  the 
cylinder,  and  great  loss  of  power  results. 

Compression  is  the  great  advance  on 
the  old  system  ;  the  greater  the  compres- 
sion before  ignition  the  more  rapid  will 


80 

be  the  transformation  of  heat  into  work 
by  a  given  movement  of  the  piston  after 
ignition,  and  consequently  the  less  will 
be  the  proportional  loss  of  heat  through 
the  sides  of  the  cylinder.  The  amount 
of  compression  is  of  course  limited  by 
the  practical  consideration  of  strength  of 
the  engine  and  leakage  of  the  piston, 
but  it  is  certain  that  compression  will  be 
carried  advantageously  to  a  much  greater 
extent  than  at  present.  The  greatest 
loss  in  the  gas  engine  is  that  of  heat 
through  the  sides  of  the  cylinder,  and 
this  is  not  astonishing  when  the  high 
temperature  of  the  flame  in  the  cylinder 
is  considered.  In  larger  engines  using 
greater  compression  and  greater  expan- 
sion it  will  be  much  reduced.  As  an  en- 
gine increases  in  size  the  volume  of  gas- 
eous mixture  used  increases  as  the  cube, 
while  the  surface  exposed  only  increases 
as  the  square,  so  that  the  proportion  of 
volume  of  gaseous  mixture  used  to  sur- 
face cooling  is  less  the  larger  the  engine 
becomes.  Taking  this  into  consideration, 
it  may  be  accepted  as  probable  that  an 


81 

engine  of  about  50  indicated  HP.  could 
be  made  to  work  on  12  cubic  feet  of  coal 
gas  per  indicated  HP.  per  hour,  or  a 
duty  of  about  32  per  cent. 

The  gas  engine  is  as  yet  in  its  infancy, 
and  many  long  years  of  work  are  neces- 
sary before  it  can  rank  with  the  steam 
engine  in  capacity  for  all  manner  of  uses ; 
but  it  can  and  will  be  made  as  managea- 
ble as  the  steam  engine  in  by  no  means 
a  remote  future.  The  time  will  come 
when  factories,  railways  amd  ships  will 
be  driven  by  gas  engines  as  efficient  as 
any  steam  engine,  and  much  more  safe 
and  economical  of  fuel.  Grs  generators 
will  replace  steam  boilers,  and  power 
will  not  be  stored  up  in  enormous  reser- 
voirs, but  generated  from  coal  direct  as 
required  by  the  engine. 

The  steam  engine  converts  so  small  an 
amount  of  the  heat  used  by  it  into  work 
that,  although  it  was  the  glory  and  honor 
of  the  first  half  of  the  century,  it  should 
be  a  standing  reproach  to  engineers  and 
scientists  of  the  present  time  having  con- 
stantly before  them  the  researches  of 
Mayer  and  Joule. 


82 
APPENDIX. 

DATA  USED  IN  THE  PAPER  ON  '  '  THE  THEORY 
OF  THE  GAS  ENGINE." 

Specific  heat  of  air  at  )  A  1  «ft 

constant  volume.  }  =       °'169  :  water  IM 
Specific  heat  of  air  at  [  _       ~  9oo 

constant  pressure  [  ~~ 
Mechanical  eqivalent ) 

of  heat  foot-lbs.  V  =1389.6 

Centigrade ) 

Specific  heat  of  air  at") 

constant  volume  | 

in  foot-lbs.  for  II          1*  a  f    +  n 

cubic  foot  at  irf        17.6  foot-lbs. 

C.  anrl   760  mm.  | 

barometer J 

Specific  heat  ( -f  air  at  ] 

constant  pressure  I 

in  foot-lbs.  for  1  I          9,  ft        <t 

cubic  foot    from  f        " 

17°    C.    and    760  | 

mm J 

Weight  of  1  cubic  ft.  ) 

of  air  at  17°   C.  [          0.0751b. 

and  760  mm ) 

Burning  completely  in  oxygen,  the  following 
substances  are  taken  as  evolving  the  noted 
amounts  of  heat  in  Centigrade  units,  per  unit 
weight  of  substance  burned. 

Hydrogen 34,170 

Carbon 8,000 

Carbonic  oxide 2,400 

Marsh  gas 13,080 

Olefiant  gas 11,900 


83 


DISCUSSION. 

Mr.  D.  CLERK  mentioned  that  Dr.  Sie- 
mens had  worked  out  the  irethod  of 
compression  used  in  engine  type  2  in 
1860  in  so  complete  a  manner  that  no 
advance  had  since  been  made  on  it  by 
any  one.  Dr.  Siemens  was  again  work- 
ing at  this  type  of  engine,  which,  from 
the  fact  of  it  using  hot  cylinder  and  re- 
generator, Mr.  Clerk  was  certain  was  the 
best  type  for  the  very  large  gas  engines 
to  be  developed  in  the  future.  With  re- 
spect to  the  cold  cylinder  engine,  of  which 
alone  he  had  treated  in  the  paper,  he 
wished  again  to  insist  on  this  :  that  the 
theory  which  sought  to  explain  the 
so-called  sustained  pressure  on  the  in- 
dicated diagram  by  the  hypothesis  of 
slow  inflammation  (erroneously  termed 
slow  combustion)  was  a  false  one.  That 
when  maximum  pressure  was  attained  in 
the  gas  engine  cylinder  it  was  certain 
that  the  whole  mass  was  completely  in- 
flamed, and  that  no  system  of  stratifica- 


84 

tion  producing  slow  inflammation  could 
do  good,  but  was  quite  opposed  to  the 
conditions  of  economy. 

Dr.  SIEMENS  said  that  one  part  of  the 
paper  dealt  with  matters  regarding  the 
mechanical  arrangement  of  gas  engines, 
and  the  other  with  a  theoretical  question, 
that  of  the  law  of  combustion.  He  would 
refer  to  the  theoretical  part  first,  because 
the  author  appeared  to  attach  great  im- 
portance to  it,  and  as  Dr.  Siemens  had 
from  time  to  time  given  a  great  amount 
of  consideration  to  the  action  of  negative 
combustion  or  dissociation,  it  might  be 
of  some  interest  to  the  members  to  see 
how  far  his  views  fell  in  with  those  set 
forth  by  the  author.  It  was  well  known 
that  by  combustion  no  unlimited  degree 
of  temperature  could  be  attained.  Thus, 
in  a  furnace  worked  at  very  high  temper- 
ature the  fuel  was  not  completely  burned 
when  it  came  in  contact  with  the  oxygen 
of  the  heated  or  non -heated  air.  The 
moment  a  certain  comparatively  high 
temperature  was  reached  the  carbon  re- 
fused to  take  up  oxygen,  or  the  hydrogen 


85 

refused  to  take  oxygen,  and  what  had 
been  called  by  Bunsen,  and,  shortly  after 
him,  by  St.  Claire  Deville,  dissociation, 
arose.  The  point  of  dissociation  was  not 
a  fixed  one  ;  partial  dissociation  came  in- 
to play  at  a  comparatively  low  tempera- 
ture, and  went  on  increasing  at  a  higher 
temperature  in  very  much  the  same  ratio 
as  vapor  density  increased  with  temper- 
ature. Thus,  if  aqueous  vapor  were 
passed  through  a  tube  at  a  sufficient 
temperature  the  whole  of  the  vapor 
would  be  dissociated,  and  the  oxygen 
and  the  hydrogen  would  be  separated. 
It  was  true,  if  these  gases  were  left  to 
themselves  they  would,  the  moment  the 
temperature  lowered  again  associate  or 
burn ;  but  if  precautions  were  taken  to 
cool  them  rapidly  after  they  had  attained 
that  high  temperature  they  would  be 
found  as  a  mixture  of  oxygen  and  hydro- 
gen simply.  The  author  had  stated  that 
the  law  which  governed  these  actions  was 
not  well  known  and  required  research, 
but  Dr.  Siemens  would  like  to  know 
whether  he  was  aware  of  the  researches 


86 

of  St.  Claire  Deville  on  the  subject.  It 
might  be  that  the  determinations  of  St. 
Claire  Deville  were  not  quite  correct,  but 
in  the  meantime  they  might  be  regarded 
as  being  so.  He  found  that  at  atmos- 
pheric pressure  the  point  of  half  dissocia- 
tion of  aqueous  vapor  arose  at  a  temper- 
ature of  2,800°  Centigrade,  and  that  of 
complete  dissociation  at  a  much  higher 
temperature.  Taking  that  law  as  deter- 
mined by  the  French  philosopher,  it  did 
seem  reasonable  to  suppose  that  when  a 
mixture  of  hydrogen  and  oxygen,  with  or 
without  a  mixture  of  nitrogen  exploded, 
the  point  was  reached  beyond  which  the 
temperature  did  not  increase,  and,  accord- 
ing to  the  author,  that  point  was  1,500° 
Centigrade.  If  such  a  temperature  was 
reached  in  a  working  cylinder  complete 
combustion  would  not  take  place  imme- 
diately, but  only  partial  combustion 
would  occur,  which  would  go  on  as  the 
temperature  diminished  by  absorption 
into  the  cylinder  or  by  expansion,  and 
that  combustion  wduld  be  completed 
only  in  the  course  of  the  stroke.  In  that 


87 

way  the  action  which  had  been  described 
with  reference  to  the  diagrams  was  rea- 
sonable enough.  With  regard  to  the 
mechanical  arrangement  of  gas  engines, 
the  author  distinguished  between  three 
types.  In  the  first,  the  mixture  of  gas 
and  air  drawn  in  at  atmospheric  pressure 
was  exploded.  In  the  second,  with  which 
the  author  had  connected  his  name  as 
that  of  the  first  proposer,  the  combustion 
was  produced  gradually ;  the  gases  were 
ignited  as  they  flowed  into  the  heating 
cylinder.  In  the  third  type,  the  gases, 
after  being  compressed  and  mixed,  were 
admitted  into1  the  working  cylinder,  and 
suddenly  exploded.  With  reference  to 
the  early  engine  which  Dr.  Siemens  con- 
structed in  1860,  the  author  had  stated 
that  it  combined  other  elements,  which 
were  entirely  wanting  in  the  gas  engines 
of  the  present  day.  The  gas  engine  of 
the  present  day,  taking  either  of  the  three 
types,  was,  in  his  opinion,  in  the  condi- 
tion of  the  steam  engine  at  the  time  of 
Newcomen.  The  ?uel  was  burnt  in  a 
cylinder  which  it  was  attempted  to  keep 


88    . 

cold  by  passing  water  over  it,  and  it  was 
easy  to  conceive  that  the  heat  so  generat- 
ed, was  only  partly  utilized  for  maintain- 
ing the  state  of  expansion  of  the  heated 
gases,  the  cold  sides  of  the  cylinder  tak- 
ing a  good  half  of  it  away  at  once,  thus 
causing  a  great  loss.  Then  there  was 
another  palpable  loss  in  these  engines. 
After  expansion  had  taken  place,  after 
half  the  heat  had  been  wasted  in  heating 
a  cylinder  which  was  intended  to  be  kept 
cool  in  order  to  allow  the  piston  to  move, 
the  gases  were  discharged  at  a  tempera- 
ture of  1,000°,  or  in  the  best  types  about 
700°.  That  amount  of  heat,  representing 
in  on^  case  one-half  and  in  the  other 
two-thirds  of  the  total  heat  generated, 
was  thrown  away.  This  was  heat  which 
could  be  saved  and  made  useful.  Instead 
of  commencing  the  combustion  at  a  tem- 
perature of  60°,  if  the  heat  of  the  outgo- 
ing gases  were  transferred  to  the  incom- 
ing gases,  combustion  might  commence 
at  a  temperature  of  nearly  1,000°,  and  the 
result  would  be  a  very  great  economy.  In 
the  engine  which  he  constructed  in  1860 


90 

(Fig.  13)  all  those  points  were  fully  taken 
into  account.  The  combustion  of  the 
gases  took  place  in  a  cylinder  without 
working  a  piston,  and  in  a  cylinder  that 
could  be  maintained  hot,  and  the  gases 
after  having  completed  expansive  action, 
communicated  their  heat  by  means  of  a 
regenerator  to  the  incoming  gases  before 
explosion  took  place.  Although  the  en- 
gine was  not  worked  with  ordinary  gas 
used  for  illumination,  but  by  a  cheaper 
kind  made  in  a  gas  producer,  he  then 
thought  that  a  gas  engine  constructed 
on  that  principle  would  prove  to  be  the 
nearest  approach  to  the  theoretical  limits 
which  could  never  be  exceeded,  but  which 
might  .exceed  the  limits  of  the  steam  en- 
gine four  or  five  fold.  The  engine  prom- 
ised to  give  very  good  results,  but 
about  the  same  time  he  began  to  give  his 
attention  to  the  production  of  intense 
heat  in  furnaces,  and  having  to  make  his 
choice  between  the  two  subjects,  he  se- 
lected the  furnace  and  the  metallurgic 
process  leading  out  of  it ;  and  that  was 
why  the  engine  had  remained  where  it 


91 

was  for  so  long  a  time.  But  now  the 
time  bad  come  when  there  was  a  greater 
demand  for  engines  of  a  smaller  kind  to 
do  their  best  in  houses  and  in  small 
works,  and  when  marine  engineers  espec- 
ially had  become  fully  alive  to  the  im- 
portance of  more  economical  arrange- 
ments. He  therefore  looked  upon  the 
question  before  the  Institution  as  one  of 
first  importance  to  engineers,  and  he 
hoped  that  it  would  be  well  discussed. 

Professor  RUCKEK  said  that  in  his  work 
on  Thermodynamics,  Mr.  Verdet  had 
published  a  calculation  of  the  theoretical 
efficiency  of  an  ideal  gas  engine.  He  as- 
sumed that  no  heat  was  lost  through  the 
sides  of  the  cylinder,  and  that  the  explo- 
sion was  so  sudden  that  the  whole  of  the 
gas  was  inflamed  before  the  piston  had 
appreciably  moved  ;  and  under  those  cir- 
cumstances he  found  that  if  the  gases 
used  were  carbonic  oxide,  and  a  sufficient 
quantity  of  air  to  burn  it  completely,  and 
if  the  whole  of  the  carbonic  oxide  was 
burnt,  the  temperature  to  which  the  gases 
would  rise,  on  the  assumption  that  their 


92 


specific  heats  remained  constant,  was 
4,388°  Centigrade.  He  found  that  the 
pressure  would  rise  from  15  Ibs.  per 
square  inch  to  215  Ibs.,  and  that  the  effi- 
ciency of  the  engine  would  be  41  per 
cent. — that  was,  that  41  per  cent  of  the 
total  amount  of  heat  produced  by  com- 
bustion of  the  gas  would  be  converted 
into  useful  work.  It  was  evident  from 
the  conditions  of  Mr.  Verdet's  problem 
that  that  was  a  purely  theoretical  calcu- 
lation. The  condition,  for  instance,  that 
no  heat  was  lost  was  one  which  could 
not  be  realized  in  practice.  About  four 
years  ago,  however,  in  the  course  of  a 
series  of  lectures  given  by  some  of  his 
colleagues  and  himself  on  coal,  he  pointed 
out  that  Mr.  Verdet's  calculation  was  not 
even  theoretically  correct;  that  Bun  sen 
had  proved  that  it  was  impossible  that  a 
mixture  of  carbonic  oxide  and  air  could 
reach  such  a  temperature  as  4,388°  Cen- 
tigrade, which  was  something  like  2,800° 
above  the  highest  temperature,  which 
Berthelot  had  shown  was  consistent  with 
Bunsen's  experiments  on  the  subject. 


93 

The  question  then  arose  what  the  effect 
of  dissociation  would  be  upon  the  gas 
engine,  and  Professor  Rucker  attempted 
to  make  a  rough  calculation  to  show  how 
important  it  might  be.  In  the  first  place, 
he  assumed  that  the  highest  temperature 
which  could  be  reached  was  that  given 
by  Bunsen's  experiments,  and  in  the  next 
that  the  specific  heats  were  constant  and 
the  inflammation  instantaneous.  With 
those  conditions  only  about  one-half  of 
the  carbonic  oxide  would  be  burned 
when  the  highest  temperature  was 
reached;  then,  as  the  piston  began  to 
move  forward  and  the  temperature  fell, 
more  would  be  consumed.  But  then 
there  was  the  very  important  question 
as  to  how  the  temperature  would 
fall,  and  in  order  to  calculate  that 
the  law  of  cooling  of  a  body  heated  to 
that  extremely  elevated  point  must  be 
known.  That,  of  course,  he  was  igno- 
rant of,  and  he  was  therefore  obliged  to 
make  a  rough  assumption.  Assuming 
that,  as  the  piston  moved  forward,  the 
gas  burned  so  as  to  keep  the  temperature 


94 


constant,  he  found  that  at  the  end  of  the 
stroke,  when  the  pressure  had  fallen  to 
that  of  the  atmosphere,  a  part  of  the  gas 
was  left  still  unconsumed.  Therefore 
in  the  half  of  the  gas  left  unburned  to 
begin  with,  there  was  sufficient  to  do  all 
work  that  was  done  while  the  piston 
was  moving  forward.  The  only  assump- 
tion he  could  make  was  that  the  tem- 
perature remained  constant ;  any  other, 
though  that  certainly  was  not  true, 
would  have  involved  some  still  more 
arbitrary  hypothesis  as  to  the  law  of 
cooling.  Making,  then,  that  rough  as- 
sumption, he  found  that  instead  of  a 
temperature  of  4,000°  Centigrade  the 
highest  reached  would  be  about  2,0l)0°; 
that  the  pressure,  instead  of  rising  to 
215  Ibs.,  would  rise  only  to  103  Ibs.; 
and  that  the  efficiency  of  the  engine 
would  be  only  25  instead  of  41  per  cent. 
That,  though  a  very  rough  calculation, 
showed  at  once  what  the  enormous  im- 
portance of  the  phenomenon  of  disso- 
ciation might  be.  It  served  the  purpose 
for  which  it  was  put  forward,  and 


95 

showed  that  in  any  theory  of  the  gas 
engine  physicists  must  make  up  their 
minds  as  to  what  part  dissociation 
played  in  it.  Passing  from  the  theo- 
retical problem  to  that  Mr.  Verdet  and 
himself  discussed,  namely,  the  case  in 
which  there  was  only  enough  air  to 
burn  the  carbonic  oxide  completely,  to 
the  practical  problem  in  which  there 
was  a  much  larger  quantity  of  air  pres- 
ent, a  case  arose  in  which  dissociation 
was  less  important.  The  larger  the 
quantity  of  air  present  the  lower  the 
highest  temperature  would  be,  and 
therefore,  probably,  the  smaller  the 
amount  of  dissociation.  St.  Claire  De- 
ville  had  shown  that  carbonic  ^cid  was 
dissociated  at  temperatures  between 
1,000°  and  1,200°,  and  water  at  temper- 
atures between  1,000°  pTid  1.10l)°  Centi- 
grade. Inasmuch,  therefore,  as  in  the 
author's  engines,  the  highest  temperature 
reached  was  about  1,500°  (or  400°  or 
500°  above  the  limits  put  by  St.  Claire 
Deville),  it  followed  that  if  his  measure- 
ment of  the  temperature  was  correct, 


96 


which  there  was  every  reason  to  believe 
it  was,  and  if  St.  Claire  Deville's  experi- 
ments were  trustworthy,  there  was  a 
certain  amount  of  dissociation  at  the 
temperatures  reached  in  his  gas  engine. 
Passing,  however,  to  the  next  question, 
namely,  how  much  dissociation  there 
was,  the  problem  was  much  more  diffi- 
cult. With  regard  to  that  subject  a 
series  of  papers  had  recently  appeared  in 
the  "  Comptes  Rendus  de  1'Academie  des 
Science,"  which  were  so  much  to  the 
point  that  he  might  be  excused  for  giving 
a  short  account  of  one  or  two  of  the  lead- 
ing results  at  which  the  experimenters 
had  arrived.  The  two  gentlemen  in 
question  were  Mr.  Mallard  (whose  ex- 
periments on  the  rate  of  propagation  of 
inflammation  in  gas  had  been  mentioned 
by  the  author)  and  a  colleague,  Mr.  Le 
Chatelier.  They  had  been  making  a 
number  of  experiments  such  as  those 
that  the  author  had  advocated  in  his 
paper.  They  had  made,  indeed,  what 
appeared  to  be  one  of  the  first  serious 
attempts  to  investigate  what  was  going 


97 

on  in  gas  heated  between  1,000°  and 
1,500°  Centigrade.  The  plan  they  adopt- 
ed was  as  follows :  They  exploded  gases 
in  an  iron  cylinder,  attached  to  which 
was  a  Bourdon  manometer ;  to  that  was 
attached  a  needle,  which  registered  the 
pressure  on  a  revolving  cylinder.  By 
reading  off  the  curve  so  obtained,  they 
got  information  as  to  the  pressure  in  the 
cylinder  at  different  times.  He  could 
not  altogether  accept  their  results  with- 
out further  confirmation.  Some  of  the 
conclusions  at  which  they  had  arrived 
were  so  striking  that  he  thought  they 
must  certainly  be  supplemented  by  other 
experiments  before  they  cculd  be  accept- 
ed. But  for  the  moment  he  would  put 
aside  all  difficulties  connected  with  the 
experiments,  and  simply  state  the  con- 
clusions. It  was  found,  dealing  with 
gases  at  very  different  temperatures,  that 
the  curves  obtained  upon  the  revolving 
cylinder  showed  a  point  of  discontinuity. 
At  the  very  highest  temperatures  the 
curves  were  somewhat  different  from 
what  they  were  at  low  temperatures,  and 


98 

the  assumption  they  made  was  that  at 
the  high  temperatures  dissociation  had 
set  in,  whereas  at  the  lower  temperatures 
there  was  no  dissociation ;  therefore  the 
law  of  cooling  would  be  different  in  the 
two  cases.  If,  however,  that  interpreta- 
tion of  the  experiments  was  accepted,  it 
would  be  found  that  the  temperatures  at 
which  dissociation  took  place  to  any  con- 
siderable extent  were  higher  than  those  he 
had  mentioned.  Thus  the  authors  stated 
that  carbonic  acid  did  not  dissociate  ap- 
preciably below  1,800°  Centigrade,  and 
that  steam-gas  did  not  dissociate  appre- 
ciably below  2,000°.  Here,  then,  there 
were  temperatures  considerably  above 
those  obtained  in  the  gas  engine ;  if, 
therefore,  the  results  in  question  were  to 
be  accepted,  dissociation  could  not  play 
a  very  important  part  in  the  matter.  But 
although  at  first  sight  the  experiments 
told  against  dissociation  taking  place  to 
any  large  extent,  in  order  to  account  for 
the  phenomena  they  observed,  Messrs. 
Mallard  and  Le  Chatelier  had  had  to  in- 
troduce another  hypothesis  which  practi- 


99 

cally  came  to  very  much  the  same  thing. 
In  all  the  earlier  calculations  upon  the 
subject  the  assumption  had  been  made 
that  the  specific  heats  of  the  gases  were 
the  same  at  high  as  at  very  low  temper- 
atures, but  within  the  last  few  years  two 
or  three  experimentalists  of  note  had 
brought  forward  results  tending  to  show 
that  the  specific  heat  of  the  gases  in- 
creased as  the  temperature  rose.  The 
two  most  important  researches  made 
upon  the  subject  were  those  by  Profes- 
sor E.  Wiedemann  and  Professor  Wull- 
ner,  the  latter  of  whom  showed  that  at 
temperatures  between  zero  and  100° 
Centigrade  there  was  an  appreciable  rise 
in  the  specific  heat  of  gases  at  a  constant 
volume.  Messrs.  Mallard  and  Le  Cha- 
telier  had  taken  that  hint,  and  they  found 
that  in  order  to  explain  the  facts  ob- 
served by  them  on  the  assumption  that 
there  was  no  dissociation,  they  must  as- 
sume an  enormous  increase  in  the  speci- 
fic heats  of  the  gases  at  high  tempera- 
tures. But  there  were  one  or  two  points 
which  appeared  to  present  difficulties  in 


100 

their  way.  Wiillner  showed  that  at  the 
temperatures  at  which  he  worked,  as 
might  be  prima  facie  expected,  the  in- 
crease was  much  greater  in  a  compound 
gas  like  water  or  carbonic  acid  than  in 
an  elementary  gas  such  as  oxygen  or  ni- 
trogen. But  Messrs.  Mallard  and  Le 
Chatelier  completely  reversed  that,  and 
found  that  the  increase  was  much  greater 
in  the  elementary  gases  than  in  the  com- 
pound ones ;  and  they  went  so  far  as  to 
show  that  oxygen  would  at  a  tempera- 
ture of  1,000°  have  a  specific  heat  no 
less  than  one  hundred  and  sixty -five 
times  greater  than  that  which  it  had  at 
zero.  That  result  was  so  astonishing 
that  it  could  not  be  accepted  without 
much  more  proof  than  had  at  present 
been  offered.  But  putting  aside  for  the 
moment  Messrs.  Mallard  and  Le  Cha- 
telier's  interpretation  of  the  experiments, 
he  wished  to  consider  what  they  meant 
from  a  wider  point  of  view,  viz ,  that 
those  gentlemen  had  come  across  a 
phenomenon  which  pointed  to  the  fact 
that  a  vast  quantity  of  heat  was  ren- 


lor 

dered  latent.  If  specific  heat  at  constant 
volume  increased,  the  meaning  of  it  must 
be  that  the  work  done  by  the  heat  was 
done  within  the  molecules  of  the  gas, 
that  the  heat  was  spent  in  separating 
or  preparing  for  separation  the  atoms 
of  those  molecules,  which  were  gradu- 
ally being  forced  asunder ;  whether  they 
were  actually  forced  asunder  or  not 
might  be  a  question,  but  a  large  amount 
of  work  was  spent  in  separating  them,  or 
preparing  to  separate  them,  by  loosening 
the  bonds  between  them ;  and  Messrs. 
Mallard  and  Le  Chatelier's  experiments 
served  as  much  as  anything  previously 
brought  forward  to  illustrate  that  point. 
He  thought  it  must  be  assumed  with  al- 
most certainty  that  a  large  quantity  of 
heat  was  rendered  latent  in  gases  at 
temperatures  between  1,000°  and  1,500° 
Centigrade.  All  would  agree  that  a  cer- 
tain amount  of  that  heat  was  spent  in 
dissociation  (for  Messrs.  Mallard  and  Le 
Chatelier  stated  that  they  harmonized 
their  results  with  those  of  St.  Claire  De- 
viile  by  supposing  that  his  experiments 


were  more  sensitive  than  their  own),  and 
the  remainder  of  the  heat  would  be 
spent,  if  not  actually  in  dissociation,  in 
preparing  for  dissociation.  There  was 
one  other  point  in  the  paper  which  he 
thought  of  interest.  The  author  had 
pointed  out  how  different  the  rate  of 
propagation  of  an  explosion  would  be  in 
the  case  of  gaseous  mixture  which  was 
confined  to  that  in  an  unenclosed  space. 
Messrs.  Mallard  and  Le  Chatelier  had 
made  experiments  on  that  point ;  they 
had  inflamed  gas  and  air  mixture  in  a 
tube  closed  at  one  end,  and  they  found 
that  when  it  was  inflamed  at  the  closed 
end  the  rate  of  propagation  was  much 
greater  than  when  it  was  inflamed  at  the 
open  end.  In  the  one  case  the  gas  was 
merely  burning  backwards  through  the 
tube,  in  the  other  the  expansion  of  the 
gases  would  spread  the  inflammation. 
So  enormous  was  the  difference,  that  in 
some  cases  they  found  that  the  rate  of 
propagation  was  one  hundred  times 
greater  when  the  gas  was  lighted  at  the 
closed  end  of  the  tube  than  when  it  was 


103 

lighted  at  the  open  end.  That  was  a 
point  which  strongly  confirmed  the  au- 
thor's view — that  inflammation  spread 
through  the  gas  almost  instantaneously. 
Although,  therefore,  one  could  not  but 
feel  that  on  those  points  there  was  a 
great  lack  of  experimental  data,  all  the 
facts  that  were  brought  together,  might, 
at  present,  be  best  explained  by  the  hy- 
pothesis that  the  inflammation  spread 
very  rapidly  through  the  gas,  and  that 
at  high  temperatures,  say  of  over  1,000°, 
a  very  large  amount  of  heat  was  rendered 
latent,  either  in  actual  dissociation  or  in 
incipient  dissociation.  Here,  then,  was 
an  explanation  of  the  curious  maintain- 
ing of  the  temperature  to  which  the  au- 
thor had  referred.  As  the  gas  cooled, 
the  latent  heat  was  given  up  and  the 
curye  was  thus  kept  up  to  a  high  tem- 
perature by  the  heat  previously  absorbed 
in  the  molecules  of  the  gas. 

Mr.  W.  E.  BOUSFIELD  did  not  propose 
to  quarrel  with  the  greater  part  of  the 
facts  stated,  which  were  for  the  most 
part  indisputable,  but  he  thought  neither 


104 

the  interpretation  which  the  author  had 
put  upon  them  could  be  upheld,  nor  the 
new  and,  to  most  of  them,  rather  start- 
ling theory  of  the  action  of  the  gas  en- 
gine which  had  been  submitted  in  the 
paper.  He  did  not  say  that  the  phenom- 
ena of  dissociation  played  no  part  in 
the  action  of  the  gas  engine ;  he  did  not 
say  that  when  the  .explosion  took  place, 
there  might  not  be  a  certain  quantity  of 
ammonia  and  a  certain  quantity  of  nitric 
acid  formed,  and  that  the  phenomena  of 
dissociation  might  not  take  place  to  a 
certain  extent ;  but  what  he  did  say  was 
that  neither  the  formation  of  nitric  acid 
nor  the  formation  of  ammonia  nor  any 
of  the  phenomena  connected  with  dis- 
sociation could  account  for  the  facts 
mentioned.  He  would  only- refer  to  two 
of  those  facts,  namely,  that  notwithstajid- 
ing  the  enormous  loss  of  heat  through 
the  walls  of  the  cylinder  of  a  gas  engine, 
amounting  to  50  per  cent,  of  the  total 
amount  of  heat  put  into  the  cylinder,  the 
curve  of  the  indicator  diagram  still  kept 
up  the  theoretical  adiabatic  line  which  it 


105 

should  follow,  supposing  the  whole  of 
the  gas  were  burned  at  the  beginning  of 
the  stroke,  and  the  walls  of  the  cylinder 
were  non-conducting.  That  was  a  start- 
ling fact  which  had  to  be  dealt  with  in 
one  way  or  another,  but  the  interpreta- 
tion of  the  fact  seemed  to  him  to  be  very 
simple,  and  even  in  the  paper  there  were 
materials  for  arriving  at  a  conclusion 
upon  it.  The  author  had  stated  that  a 
mixture  of  gas  and  air  took  a  certain  time 
to  ignite,  that  if  ignition  was  set  up  at 
one  point  it  took  a  certain  time  before  it 
was  communicated  to  another.  There 
was  also  the  further  fact  that  at  the  rate 
of  communication  of  the  ignition  from 
one  point  of  the  dilute  mixture  to  an- 
other varied  directly  with  the  amount  of 
dilution  of  the  mixture.  Supposing  for 
instance  there  was  a  mixture  of  gas  and 
air  in  the  right  proportions  for  explosion, 
the  ignition  would  take  place  at  a  certain 
speed ;  if  more  air  was  put  in,  the  rate 
would  be  less  ;  the  greater  the  quantity, 
the  less  the  rate  at  which  the  ignition 
traveled.  That  simple  fact  he  thought 


106 

sufficient  to  account  for  all  the  phenom- 
ena. The  diagram  which  the  author 
had  given  (Fig.  9)  seemed  to  him,  taken 
in  conjunction  with  the  fact  to  which  he 
had  referred,  to  support  the  theory 
which  had  been  put  forward  by  Mr. 
Otto  and  by  the  scientific  world  in  gen- 
eral. In  the  Otto  gas  engine  the  charge 
varied  from  a  charge  which  was  an  ex- 
plosive mixture  at  the  point  of  ignition 
to  a  charge  which  was  merely  an  inert 
fluid  near  the  piston.  When  ignition 
took  place,  there  was  an  explosion  close 
to  the  point  of  ignition  that  was  gradu- 
ally communicated  throughout  the  mass 
of  the  cylinder.  As  the  ignition  got 
further  away  from  the  primary  point  of 
ignition  the  rate  of  transmission  became 
slower,  and  if  the  engine  were  not 
worked  too  fast  the  ignition  should 
gradually  catch  up  the  piston  during  its 
travel,  all  the  combustible  gas  being  thus 
consumed.  When  the  engine  was  worked 
properly  the  rate  of  ignition  and  the 
speed  of  the  engine  ought  to  be  so  timed 
that  the  whole  of  the  gaseous  contents 


107 

of  the  cylinder  should  have  been  burned 
out  and  have  done  their  work  some  little 
time  before  the  exhaust  took  place,  so 
that  their  full  effect  could  be  seen  in  the 
working  of  the  engine.  This  was  the 
theory  of  the  Otto  engine.  What  was 
the  theory  which  the  author  had  put  for- 
ward ?  He  had  stated  that  when  gases 
combined  a  high  temperature  was  set 
up ;  that  a  high  temperature  prevented 
combination  of  the  gases  beyond  a  cer- 
tain point ;  and  therefore,  at  the  moment 
of  ignition,  there  existed  in  the  cylinder 
a  body  of  gases  heated  to  a  temperature 
beyond  the  point  of  dissociation.  A  part 
of  those  gases  being  in  a  state  of  com- 
bination, and  having  therefore  given  out 
a  heat  which  was  doing  the  work  of  push- 
ing the  piston ;  a  part  of  the  gases,  not 
being  in  a  state  of  combination,  being 
ready  to  combine  as  soon  as  the  tempera- 
ture was  lowered  to  such  a  point  that 
they  could  combine  and  give  out  work. 
Looking  at  that  theory,  it  seemed  as  if 
the  point  involved  was  a  mere  question  of 
words,  so  far  as  regarded  any  question 


108 

of  infringement.  In  either  case,  what 
had  to  be  dealt  with  was  this.  The  adi- 
abatic  line  represented  the  line  which 
was  traced  out  upon  the  indicator  dia- 
gram when  no  heat  escaped  through  the 
walls  of  the  cylinder,  and  when  the  whole 
heat  which  the  gases  lost  was  converted 
into  work  done  by  the  piston ;  so  that, 
taking  an  indicator  diagram,  and  finding 
the  work  done  as  represented  by  the 
area  included  by  the  curve,  the  ordinates 
and  the  atmospheric  line,  this  work  ought 
to  be  equal  to  the  quantity  of  heat,  rep- 
resented in  foot-lbs.,  which  had  been 
given  out  by  the  gas,  as  shown  by  the 
difference  of  temperatures  and  specific 
heat  of  the  gas.  Of  course,  when  heat 
was  escaping  through  the  cylinder,  and 
when  the  adiabatic  line  was  still  kept  up 
to,  a  considerable  amount  of  energy 
must  be  developed  somewhere,  in  order 
to  make  up  for  the  energy  which  went 
through  the  walls  of  the  cylinder.  The 
only  source  of  energy  in  the  gas  engine 
was  the  union  of  combustible  gases  and 
oxygen,  and  it  followed  that  that  con- 


109 

stant  supply  of  energy  must  come  from 
the  combustion  of  the  gases  within  the 
cylinder.  It  was  therefore  a  mere  ques- 
tion of  words,  because,  whether  the  en- 
ergy was  developed  by  the  combustion 
of  the  gases  which  took  place  through 
the  lowering  of  the  temperature  below 
the  point  of  dissociation,  or  whether 
that  energy  was  given  out  through  the 
combustion  of  the  gases  which  took 
place  from  the  communication  through 
the  mass  of  an  ignition  which  traveled 
slowly  through  it,  in  either  case  it  was 
a  gradual  combustion.  It  was  therefore 
a  mere  question  of  theory,  and  he  did 
not  see  in  what  way  it  could  affect  the 
question  of  infringement.  If  Messrs. 
Orossley  and  Mr.  Otto  had  overlooked 
the  theory  of  dissociation,  and  had  at- 
tributed the  gradual  combustion  to 
something  which  they  ought  not  to  have 
attributed  it  to,  he  did  not  see  how  it 
could  affect  their  position.  The  real 
point  of  difference,  however,  in  a  scien- 
tific point  of  view,  between  the  author- 
and  himself  was  this.  The  author  as- 


110 

sumed  that  the  ignition  was  quickly 
transmitted  through  the  cylinder,  and 
took  place  almost  at  once  near  the  be- 
ginning of  the  stroke,  and  that  the  ulti- 
mate combustion  was  due  to  dissocia- 
tion ;  whereas  Mr.  Bousfield  thought 
with  Mr.  Otto  and  many  others  that  the 
cause  of  the  supply  of  energy  was  the 
gradual  communication  of  ignition 
through  the  contents  of  the  cylinder. 
The  author  assumed  gratuitously  that 
when  the  point  of  maximum  pressure 
was  reached,  that  point  marked  the 
communication  of  ignition  throughout 
the  whole  of  the  cylinder.  That  there 
was  absolutely  no  ground  for  that  as- 
sumption could  be  very  readily  shown. 
Neglecting  for  the  moment  the  loss  of 
heat  through  the  walls  of  the  cylinder, 
the  curve  representing  the  increase  of 
pressure  due  to  the  combustion  of  the 
gas,  supposing  the  gases  to  combine  at 
the  same  rate  as  they  actually  did,  but 
not  to  be  allowed  to  expand  by  the  mo- 
tion of  the  piston,  could  be  ascertained 
thus  : — Divide  the  atmospheric  line  (Fig. 


Ill 

14)  into  spaces  AB,  BC,  CD,  DE,  &c., 
representing  equal  small  spaces  of  time 
or  equal  parts  of  a  revolution.  From 
each  of  the  points  A,  B,  C,  &c.,  raise 
ordinates  AL,  BF,  CG,  &c.,  to  meet  the 
indicator  curve  in  the  points  F,  G,  H, 
&c.,  and  from  the  points  F,  G,  H,  &c., 
draw  adiabatics  to  meet  AL  in  L,  M, 
N,  &c.  From  L,  M,  N,  &c.,  draw  lines 
parallel  to  AB  to  meet  their  correspond- 
ing ordinates  in  P,  Q,  K,  &c.  Then  the 
curve  P,  Q,  B,  &c.,  drawn  through  these 
points,  would  be  a  curve,  the  ordinates 
of  which  were  proportional  to  the  press- 
ure at  any  time  of  the  contents  of  the 
cylinder,  supposing  these  contents  to  re- 
main confined  in  the  space  at  the  end 
of  the  cylinder,  and  not  allowed  to  ex- 
pand, and  supposing  the  rate  of  com- 
bustion of  these  contents  to  be  exactly 
the  same  as  actually  occurred.  This 
curve,  therefore,  showed  the  actual  prog- 
ress of  the  combustion  deduced  from 
the  working  diagram.  Even  neglecting 
the  loss  of  heat  through  the  walls  of  the 
cylinder,  it  would  be  seen  that  this  curve 


112 


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113 

ascended  to  a  point  past  the  point  of 
maximum  pressure,  viz.,  till  the  point 
K,  at  the  commencement  of  the  part  KY 
(which  was  supposed  to  be  exactly  adi- 
abatic)  was  reached.  From  the  point  S 
this  curve  became  in  the  actual  diagram 
a  straight  line  parallel  to  AB.  If,  how- 
ever, the  theoretical  diagram,  allowing 
for  loss  by  conduction,  were  taken,  the 
curve  PQRS  would  ascend  throughout 
the  stroke.  Hence  the  maximum  point 
on  the  diagram  was  simply  the  point 
where  the  increase  of  pressure  due  to 
combustion  was  balanced  by  the  decrease 
of  pressure  due  to  the  forward  motion 
of  the  piston,  and  there  was  no  reason 
for  saying  that  this  maximum  point  cor- 
responded to  complete  ignition.  He  had 
had  an  opportunity  of  taking  diagrams 
from  the  Otto  gas  engine,  which  Pro- 
fessor Ayrton  had  at  the  City  Guilds 
Technical  School,  Cowper  Street.  The 
engine  was  designed  for  the  electric 
light,  and  the  cam,  controlled  by  the 
governor,  was  made  in  a  series  of  steps. 
He  therefore  had  the  governor  taken 


114 

off,  and  the  cam  and  the  roller  on 
which  it  acted  so  arranged  that  it  should 
work  independently  of  the  velocity  of 
the  engine  on  a  given  step,  so  that  the 
charge  might  be,  as  nearly  as  possible, 
the  same  at  all  speeds.  And  he  varied 
the  load  by  braking  the  fly-wheel.  The 
two  sets  of  diagrams  were  taken,  one  at 
a  speed  of  one  hundred  revolutions,  and 
the  other  at  two  hundred ;  thus  might 
be  seen  the  effect  which  must  be  due  to 
the  phenomenon  he  had  spoken  of — the 
ignition  traveling  gradually ;  it  could  not 
be  due  to  dissociation,  for  the  reason 
which  Mr.  Imray  had  pointed  out.  In 
the  diagrams  the  phenomena  of  dissoci- 
ation ought  to  be  exaggerated  at  the 
higher  temperature,  but  instead  of  that, 
it  would  be  seen  that  the  effects  at- 
tributed to  dissociation  were  less  at  the 
higher  temperature  where  dissociation 
should  be  most  active,  and  greatest  at 
temperature  below  the  point  of  dissoci- 
ation ;  he  therefore  did  not  see  why  the 
results  should  be  attributed  to  the  phe- 
nomena of  dissociation,  when  they  could 


115 

be  perfectly  explained  by  the  rate  of 
progress  of  ignition  through  the  cylinder. 
With  the  full  charge  at  one  hundred 
and  at  two  hundred  revolutions  the 
effect  of  difference  of  speed  was  small, 
as  shown  by  the  two  diagrams  in  Fig. 
15.  In  that  case,  the  rate  at  which  the 
ignition  went  through  the  cylinder  was 
so  great  that  it  only  made  a  very  little 
difference  in  the  curve  when  the  rate  got 
up  to  two  hundred  revolutions.  He  then 
fixed  the  roller  on  the  third  step,  when 
there  was  a  less  charge  of  gas.  The 
diagram,  Fig.  16,  showed  the  hundred- 
revolution  curve,  in  which  the  gas  had 
time  to  explode,  and  to  carry  the  pencil 
indicator  up  to  the  maximum  point,  and 
then  down  to  the  adiabetic  line.  Going 
to  two  hundred  revolutions  with  the 
more  dilute  mixture,  the  rate  of  propaga- 
tion of  ignition  was  slower  ;  therefore  at 
that  speed,  although  the  temperature 
was  less,  dissociation  would  have  much 
more  to  do.  The  effect  was  much  more 
marked,  simply  from  the  dilution  of  the 
mixture  ;  there  was  therefore  a  less  rate 


116 


lO 

bb 


of  propagation  of  ignition,  and  the  curve 
took  the  form  shown  in  the  diagram. 
Fig.  17  showed  the  same  effects  on  the 
diagram  when  the  curve  roller  was  on 


118 

the  second  step,  and  consequently  still 
less  gas  was  admitted.  The  five  super- 
posed diagrams  were  taken  at  speeds  be- 
tween one  hundred  and  two  hundred 
revolutions  per  minute.  It  would  be 
observed  that  the  curve  at  the  higher 
speed  generally  went  outside  the  door. 
There  was  less  work  done  at  the  begin- 
ning, and  more  gas  to  be  combined  at 
the  end,  and  therefore  a  greater  amount 
of  work  done  at  the  end  of  the  stroke. 
He  did  not  wish  to  carry  the  comparison 
all  the  way  through,  but  he  would  leave 
it  to  the  author  to  show  how  he  ex- 
plained the  diagrams  under  the  dissoci- 
ation theory.  In  Fig.  18  there  was  the 
least  amount  of  gas  with  which  the  en- 
gine would  work,  and  the  speed  was  one 
hundred  and  thirty  revoluions.  The 
compression  was  30  Ibs. ;  the  compres- 
sion line  was  the  same  as  the  others. 
The  working  line  was  a  line  nearly  par- 
allel with  the  atmospheric  line,  but 
slightly  rising,  and  at  the  end  the  ig- 
nition was  not  finished,  indeed,  in  this 
case,  if  a  light  was  applied  to  the  ex- 


I 


haust  the  contents  would  explode.  Ac- 
cording to  the  author's  theory,  that 
maximum  point  near  the  end  of  the 
stroke  in  the  last  diagram  was  a  point 


120 


CO 

bJD 


121 

where  the  ignition  was  complete,  and 
therefore  all  the  gas  should  have  combined 
at  that  low  temperature  where  no  dis- 
sociation could  take  place.  Those  were 
points  which  the  author  would  have  to 
meet  in  order  to  support  his  theory. 
Many  of  the  facts  mentioned  by  the 
author  were  incontestable,  and  his  chief 
dispute  with  him  was  as  to  the  interpre- 
tation he  had  put  upon  them.  The  au- 
thor had  said  nothing  against  the  theory 
to  which  he  had  referred  except  that  it 
was  new,  no  argument  whatever  being 
advanced  against  it.  The  author  stated, 
"From  the  considerations  advanced  in 
the  course  of  this  paper,  it  will  be  seen 
that  the  cause  of  the  comparative  effi- 
ciency of  the  modern  type  of  gas  engines 
over  the  old  Lenoir  and  Hugon  is  to  be 
summed  up  in  one  word,  'compression.'" 
He  had  not  had  time  to  go  carefully 
through  the  diagrams ;  but  he  did  not 
think  that  they  were  fair  comparisons, 
and  he  thought  that  other  elements 
ought  to  have  been  taken  into  account. 
The  author  had  given  the  old  Lenoir, 


122 

and  had  stated  that  the  temperature  was 
the  same,  that  the  mixture  of  gas  was 
the  same,  and  that  the  great  advantage 
over  the  Lenoir  was  compression.  Mr. 
Bousfield  might  be  permitted  to  point 
out  that,  in  the  Lenoir  engine,  the  adi- 
abatic  line  was  much  above  the  actual 
line.  It  would  be  fairer  to  substitute 
the  word  "  dilution  "  for  "  compression," 
so  that  the  sentence  would  read:  "The 
cause  of  the  comparative  efficiency  of 
the  modern  type  of  gas  engines  over  the 
old  Lenoir  and  Hugon  is  to  be  summed 
in  one  word,  '  dilution.* "  The  fact,  how- 
ever, was  that  it  could  not  be  summed 
up  in  one  word ;  the  two  should  be  taken 
together,  compression  and  dilution. 
The  author  further  stated:  "The  pro- 
portion of  gas  to  air  is  the  same  in  the 
modern  gas  engine  as  was  formerly  used 
in  the  Lenoir."  He  did  not  think  so. 
He  believed  that  the  Lenoir  worked  up 
to  13  to  1,  and  could  not  get  further. 
He  did  not  know  what  proportion  Otto 
used,  but  it  was  considerably  more  than 
that.  It  was  also  stated  that  the  time 


123 

taken  to  ignite  the  mixture  was  the  same ; 
but  that  was  a  gratuitous  assumption. 
The  author  said :  "  The  cause  of  the  sus- 
tained pressure  shown  by  the  diagrams  is 
not  slow  inflammation  (or  slow  combustion 
as  it  has  been  called),  but  the  dissociation 
of  the  products  of  combustion,  and  their 
gradual  combination  as  the  temperature 
falls,  and  combination  becomes  possible. 
This  takes  place  in  any  gas  engine,  whether 
using  a  dilute  mixture  or  not,  whether 
using  pressure  before  ignition  or  not, 
and  indeed  it  takes  place  to  a  greater  ex- 
tent in  a  strong  explosive  mixture  than 
in  a  weak  one."  Dissociation  took  place 
far  more  at  high  temperatures  than  at 
low;  and  if  the  author's  application  of 
the  theory  were  correct  the  phenomena 
of  dissociation  ought  to  play  a  much 
greater  part  at  high  than  at  low  tem- 
peratures. He  had  pointed  out  that  this 
was  not  so  in  the  diagrams,  and  that  it 
was  not  so  with  Lenoir's  explosive  en- 
gines where  the  curve  fell  far  below  the 
adiabatic  line.  The  paper  contained 
other  matters  which  he  had  not  time  to 


124 

dwell  upon ;  but  he  thought  he  had  said 
enough  to  challenge  the  author  to.  show 
how  he  got  rid  of  the  old  theory,  and  ex- 
plained the  facts  to  which  Mr.  Bousfield 
had  referred. 

Dr.  JOHN  HOPKINSON  said  a  very  inter- 
esting question  had  been  discussed  by 
Professor  Kiicker  and  Mr.  Bousfield,  to 
which  he  desired  to  refer.  The  author 
maintained  that  the  ignition  of  the  mix- 
ture of  gases  had  extended  throughout 
the  whole  space  at  a  time  approximately 
represented  by  the  point  of  maximum 
pressure.  Others,  on  the  contrary, 
maintained  that  the  ignition  had  not  ex- 
tended through  that  space  by  that  time, 
but  that  it  took  a  time  lasting  into  the 
descending  part  of  the  indicator  diagram 
before  the  disturbance  had  extended 
throughout  the  whole  of  that  space. 
The  author  attributed  the  maintenance 
of  the  temperature  during  the  latter 
part  of  the  curve,  and  its  approximation 
to  an  adiabatic  curve,  to  the  gradual 
combination  of  the  gas  through  the  mass, 
that  combination  not  occurring  com- 


125 

pletely  in  the  first  instance  owing  to  the 
temperature  being  so  high  that  a  certain 
measure  of  dissociation  occurred,  or  at 
all  events  so  high  that  comptete  com- 
bination could  not  occur.  He  thought 
that  the  question  might  be  submitted  to 
a  crucial  test.  Suppose  the  opponents 
of  the  author  were  right,  if  a  given  mix- 
ture of  air  and  gases  were  exploded  in  a 
gas  engine  revolving  at  a  low  rate  of 
speed  or  in  an  entirely  closed  space,  it 
would  be  expected  that  the  maximum 
pressure  would  approximate  to  that 
calculated  from  the  heat  due  to  the  com- 
bustion of  the  gas  present  and  the  tem- 
perature resulting  therefrom.  If  the 
gine  were  running  slowly,  or  if  the  ex- 
plosion were  made  in  a  completely 
confined  space,  the  pressure  would  be 
expected  to  rise  to  a  point  very  greatly 
in  excess  of  that  observed  in  the  gas 
engine  running  at  »its  normal  speed. 
Whether  that  were  so  he  did  not  know. 
The  experiment  might  be  objected  to  on 
the  ground  that  when  the  engine  was 
running  slowly  there  was  a  great  loss  of 


126 

heat  through  the  walls  of  the  cylinder. 
That  would  give  rise  to  a  second  crucial 
experiment.  If  the  author  was  right  the 
maximum  pressure  in  large  and  small  en- 
gines would  be  about  the  same ;  if  those 
who  differed  from  him  were  right,  in  a 
large  engine  the  maximum  pressure  would 
probably  be  greatly  in  excess  of  that  in 
a  small  engine,  there  being  less  loss  of 
heat  through  the  walls '  of  the  cylinder. 
What  the  answer  might  be  he  did  not  know, 
but  it  appeared  to  him  that  there  were 
there  the  elements  of  settling  the  ques- 
tion. The  author  divided  gas  engines 
into  three  classes,  and  had  made  a  com- 
parison of  their  theoretical  efficiency. 
In  the  second  the  mixtures  were  ad- 
mitted into  the  cylinder,  and,  without 
increase  of  pressure,  the  heat  produced 
was  devoted  to  increase  of  volume.  In 
the  third  the  mixtures  were  introduced 
into  the  cylinder,  and  then  burned  with 
an  increase  of  pressure  without  immedi- 
ate increase  of  volume ;  and  in  those  two 
cases  he  took,  for  the  purpose  of  com- 
parison, different  maximum  pressures. 


127 

In  the  second  type  he  took  a  pressure 
of  7(>  Ibs.,  and  in  the  third  over  200  Ibs. 
Prima  facie  it  would  seem  natural,  in 
order  to  make  a  fair  comparison,  that  the 
same  maximum  pressure  should  be  taken 
in  the  two  cases.  Probably  the  author 
had  a  good  reason  to  justify  his  making 
a  comparison  on.  that  basis,  and,  per- 
haps, in  his  reply  he  would  point  it  out. 
He  agreed  with  those  who  had  so  often 
spoken  on  the  subject  of  the  gas  engine 
that  in  that  engine  lay  the  future  of  the 
production  of  power  from  heat  of  com- 
bustion. It  was  quite  in  its  infancy,  and 
it  had  already  beaten  the  best  steam  en- 
gines in  economy  of  fuel,  for  the  obvious 
reason  that  it  was  practicable  to  use 
with  it  much  higher  temperatures.  The 
steam  engine  tolerably  approximated  to 
the  theoretical  efficiency  that  might  be 
expected  from  it,  having  regard  to  the 
temperatures  between  which  it  was  prac- 
ticable to  work  it.  That  was  not  the  case 
with  the  gas  engine,  there  being  still  a 
very  large  margin  for  practical  improve- 
ment. Having  regard  to  the  very  short 


128 

time  during  which  gas  engines  had  been 
used,  he  thought  that  practical  improve- 
ments would  take  place,  and  that,  when 
such  difficulties  as  that  of  starting  a 
large  engine  as  conveniently  as  steam  en- 
gines could  be  started  had  been  over- 
come, the  gas  engine  would  supersede 
the  steam  engine. 

Mr.  E.  F.  BAMBER  wished  the  author 
had  commenced  his  paper  with  that  por- 
tion which  treated  of  the  analysis  of  the 
gas,  and  had  given  the  mechanical  equiv- 
alent of  a  unit  of  the  same  both  in  the 
pure  and  diluted  state.  If  the  explana- 
tion had  then  followed,  that  the  mechan- 
ical equivalent  of  the  latent  heat  of  ex- 
pansion per  unit  of  the  gaseous  mixture 
per  degree  of  temperature  was  nearly  the 
same  as  for  atmospheric  air,  the  reason 
why  the  gas  engine  might  be  considered 
in  theory  as  an  air  engine  would  have 
been  clearer,  namely,  that  the  adiabatic 
curve,  or  curve  of  no*  transmission  of 
heat,  was  nearly  the  same  for  both.  The 
author  commenced  by  an  attack  upon  the 
steam  engine.  Much  heat  was  required 


129 

in  evaporating  water  whose  specific  heat 
was  high,  and  hence  the  efficiency  of  the 
steam  engine  was  low,  and  something 
better  was  needed ;  whereas  it  was  clearly 
proved  by  Eankine,  a  quarter  of  a  century 
ago,  that  the  maximum  efficiency  of  a 
theoretically  perfect  heat  engine,  working 
between  given  limits  of  temperature, 
was  equal  to  the  ratio  of  the  range  of 
temperature  to  the  higher  absolute  limit 
of  temperature,  and  quite  independent 
of  the  fluid  employed.  Raising  the  tem- 
perature entirely  by  compression  or  using 
regenerators  were  the  two  means  by 
which  the  actual  efficiency  might  be  made 
to  approach  the  maximum  limit.  The 
author  believed  in  compression,  but  his 
method  of  defence  of  it  and  his  illustra- 
tions of  its  advantages  did  not  appear  to 
be  quite  correct.  He  took  three  types  of 
engine :  the  first  and  third  were  ex- 
plosive gas  engines ;  the  second  was 
worked  at  constant  pressure,  and  these 
he  treated  as  air  engines.  The  first  and 
second  were  worked  between  the  same 
limits  of  temperature,  but  in  the  second 


130 

compression  was  employed.  What  the 
author  wished  to  prove  by  the  theoretical 
diagrams  of  these  types  was  that  the 
constant-pressure  engine  using  com- 
press'on  was  more  theoretically  perfect 
than  an  explosive  engine  using  none, 
whilst  Jin  explosive  engine  using  compres- 
sion was  the  best  of  the  three.  But  he 
had  shown  by  type  No.  2,  that  by  the 
use  of  compression  ai-  efficiency  could  be 
attained  higher  than  the  maximum  ef- 
ficiency of  a  perfect  heat  engine,  which 
seemed  to  require  some  explanation. 

The  maximum  was  equal  to  -J ?  in  ab- 

r, 

solute  degrees  of  temperature,  and  was 
for  1,537°  Centigrade  and  1,089°  Centi- 
grade equal  to  0.247  for  both  types ; 
whereas  the  author  made  it  0.21  for  the 
first  and  0.36  for  the  second.  The  author 
allowed  that  type  No  1  would  be  im- 
proved by  further  expansion,  but  that 
that  would  require  a  vacuum  pump  and 
condenser ;  yet  surely  it  made  no  differ- 
ence, so  long  as  they  both  consumed  the 
same  quantity  of  heat,  whether  a  com- 


131 

pression  pump  was  used  at  the  beginning 
or  a  vacuum  pump  at  the  end  of  the 
stroke,  whilst  indeed  there  might  be  theo- 
retical reasons  in  favor  of  the  latter. 
Types  1  and  3  were  respectively  worked 
without  and  with  compression  ;  they  were 
both  explosive  engines,  and  the  efficiency 
of  the  latter  was  made  double  that  of  the 
former,  but  the  latter  was  made  to  dis- 
charge at  648°  Centigrade,  and  the 
former  at  1,089°  Centigrade.  If  these 
figures  had  been  reversed,  so  would  have 
been  the  efficiencies.  Had  the  author 
explained  that  there  was  a  certain  maxi- 
mum efficiency  for  heat  engines,  and  that 
by  means  of  compression  a  larger  per- 
centage of  that  maximum  could  be  at- 
tained than  without  it,  there  would  have 
been  no  reason  for  objection  ;  but  that 
was  a  very  different  thing  from  trying  to 
show  that  it  was  possible  to  obtain  more 
than  the  maximum  efficiency  of  a  theo- 
retically perfect  heat  engine. 

The  real  value  of  the  gas  engine  was, 
that  it  contained  the  furnace  and  engine 
in  one ;  thus  the  necessary  heat  lost  in 


132 

the  furnace  to  make  a  draught,  and  the 
unnecessary  loss  of  heat  by  radiation 
from  a  large  steam  boiler  were  both 
avoided  in  the  gas  engine,  and,  finally, 
the  gas  engine » could  be  used  safety  at 
a  maximum  limit  of  temperature,  which 
could  not  be  employed  in  the  steam  en- 
gine. There  was  no  doubt  a  great  future 
for  this  class  of  motor. 

Sir  WILLIAM  THOMSON  said  that  he  had 
recently  seen  a  very  interesting  experi- 
ment made  by  the  author  with  a  gas 
engine  at  Glasgow,  which  he  thought  had 
a  most  important  bearing  on  the  mode  of 
action  of  the  gas  in  the  cylinder.  The 
experiment  was  made  in  the  presence  of 
his  brother  Professor  James  Thomson 
and  Professors  Jack  and  Ferguson  (of 
Mathematics  and  Chemistry  in  the  Uni- 
versity of  Glasgow),  who  were  all  much 
interested  in  the  inquiry.  The  object 
was  to  test  the  nature  of  the  mixture  in 
close  proximity  to  the  piston,  so  as  to  be 
able  to  form  some  idea  as  to  whether  or 
not  the  explosion  took  place  through  the 
whole  space ;  to  be  judged  by  finding 


133 

whether,  right  up  to  contact  with  the 
piston,  gas  and  air  were  present  in  pro- 
portions suitable  for  combustion.  He 
need  not  enter  into  details  as  to  the  way 
in  which  the  experiment  ,was  made,  but 
he  might  say,  in  a  general  way,  that  while 
the  piston  was  being  pressed  in  to  con- 
dense the  mixture  at  a  definite  point  of 
the  stroke,  communication  was  made  with 
the  cylinder.  The  small  experimental 
cylinder  and  piston  were  placed  in  proper 
position,  in  communication  with  an  aper- 
ture bored  for  the  purpose  in  the  main 
cylinder.  The  author  of  the  paper 
would  be  able  to  explain  the  details  better 
than  Sir  William  Thomson  could.  It  was 
sufficient  to  say  that  by  an  automatic 
arrangement,  worked  mechanically  from 
the  cross-head,  the  communication  was 
made  exactly  at  one  definite  point  of  the 
stroke,  and  the  experimental  piston  was 
pressed  up  in  the  cylinder  so  as  to  let  it 
fill.  At  any  time  afterwards  the  stop- 
cock could  be  opened  by  hand,  and  the 
nature  of  the  contents  tested.  In  every 
case  the  contents  were  found  to  be  ex- 


134 

plosive — an  explosive  mixture  of  gas  and 
.air — proving  that  up  to  the  very  point, 
which  he  understood  was  within  about  an 
inch  from  the  piston,  coal  gas  was  present 
in  suitable  proportions  for  producing  an 
explosion.  There  was  one  other  matter 
to  which  he  wished  to  refer,  which  had 
been  noticed  in  the  discussion.  There 
appeared  to  be  some  difference  of  opinion 
upon  it,  but  to  his  mind  it  scarcely  ap- 
peared open  to  doubt  — that  the  diagram, 
which  showed  an  exceedingly  sudden  rise 
and  a  gradual  fall,  proved  that  combus- 
tion was  practically  complete  at  a  point 
corresponding  to  the  summit  of  the 
curve.  Literally  and  precisely  the  instant 
of  the  maximum  of  the  curve  was  that 
at  which  the  rate  of  loss  of  pressure  by 
expansion,  the  much  smaller  rate  of  loss 
of  pressure  by  loss  of  heat  carried  by 
convection  of  the  fluid  to  the  solid  boun. 
dary  and  out  by  conduction  through  the 
metal,  were  exactly  counterbalanced  by 
the  rate  of  combustion  still  going  on.  It 
seemed  certain  that  the  rate  of  loss  by 
the  two  causes  he  had  indicated  was  ex- 


135 

ceedingly  small  in  comparison  with  the 
rate  of  rise  by  the  initial  progress  of  the 
explosion ;  therefore,  practically  speaking, 
the  maximum  of  the  curve  indicated  truly 
the  instant  when  the  combustion  was  as 
complete  as  dissociation  at  the  highest 
tempearature  attained  allowed  it  to  be. 

Mr.  D.  CLERK,  in  reply  upon  the  dis- 
cussion, said  that  two  of  the  speakers 
seemed  to  think  that  the  question  at  issue 
was  one  of  infringement  of  patent,  but 
he  desired  to  arrive  at  the  truth,  apart 
from  mere  questions  of  personal  interest. 
The  question  of  infringement  was  to  him 
one  of  complete  indifference. 

The  question  he  was  anxious  about 
was  the  purely  scientific  one.  Was  his 
theory  of  the  action  of  the  gas  engine  the 
true  one,  or  was  it  Mr.  Otto's  ?  This  mat- 
ter might  appear  to  some  persons  a  small 
one,  but  he  considered  it  of  vital  interest, 
being  convinced  that  not  many  years 
hence  the  gas  engine  would  have  a  science 
of  itb  own,  and  scientific  names  connected 
with  it  as  much  honored  as  any  ever 
linked  with  the  steam  engine.  Dr.  Sie- 


136 

mens  bad  fully  corroborated  his  view  of 
dissociation,  and  in  the  effect  it  had  on 
the  gas  engine  diagram,  in  preventing  the 
more   rapid   fall,    which    must  otherwise 
occur  ;  but  he  did  not  agree  with  him  in 
the  necessity  for  further  research  on  dis- 
sociation,    believing      that      St.      Claire 
Deville's   work   was    sufficient.     Dr.  Sie- 
mens   would    observe    that    St.      Claire 
Deville's  researches  were   referred  to  in 
the  paper;    but  what  he  asked  for  had 
never  to  his  knowledge  been  published, 
that  was  a  complete  curve  of  the  dissoci- 
ation   of   water   and   carbonic  acid.     St. 
Claire   Deville's  results  were   more  of  a 
qualitative  than  of  a  quantitative  nature. 
He  feared  that  the  method  used  was  not 
capable  of  the  necessary  accuracy. 

He  thoroughly  believed  that  the  engine 
for  the  very  large  powers  to  be  construct- 
ed in  future  must  be  of  one  type  2,  with 
hot  chamber  or  cylinder,  and  regenerative 
contrivance  in  some  form  ;  indeed,  about 
two  years  ago  he  constructed  and  experi- 
mented with  such  an  engine,  and  he  was 
continuing  his  experiments. 


137 

The  mechanical  difficulties  were  much 
greater  than  in  the  cold  cylinder,  type  3. 
It  must  be  remembered  that  the  cold 
cylinder  gas  engine  was  the  engine  of  the 
present,  and  it  was  most  satisfactory  that 
even  with  the  small  sizes  so  high  a  duty 
should  be  obtained.  It  proved  that  when 
larger  engines  were  made  a  much  higher 
duty  might  be  expected.  The  theory  of 
the  cold  cylinder  engine  did  not  allow  of 
the  application  of  any  regenerative  con- 
trivance, and  consequently  arrangements 
must  be  made  to  get  the  greatest  possi- 
ble fall  of  temperature  due  to  work  done. 
A  very  interesting  account  had  been 
given  by  Professor  R acker  of  his  view  of 
the  problem,  and  the  necessity  of  correct- 
ing the  calculations  of  previous  observers 
in  the  light  of  present  knowledge  of  the 
laws  of  combustion  had  been  demonstrat- 
ed. It  was  satisfactory  that  Professor 
Eiicker  so  thoroughly  agreed  with  him 
on  the  necessity  for  considering  dissocia- 
tion in  any  theory  of  the  gas  engine,  and 
had  independently  arrived  at  similar  con- 
clusions. The  experiments  of  Messrs. 


138 

Mallard  and  Le  Chatelier  corroborated 
those  of  Professor  Bunsen  in  this,  that  at 
the  high  temperature  of  combustion,  a 
large  amount  of  heat  was  rendered  latent. 
So  striking  a  fact  could  hardly  have 
escaped  the  notice  of  many  other  experi- 
menters who  might  not  have  published 
their  results.  He  had  noticed  it  about 
five  years  ago,  while  making  experiments 
on  the  maximum  pressure  obtainable  from 
a  pure  explosive  mixture  of  gas  and  air. 
A  cylinder  9  inches  in  diameter  and  9 
inches  long,  was  filled  with  a  mixture  of 
gas  and  air  in  the  proportions  for  maxi- 
mum explosive  effect,  and  ignited  the 
mixture  by  means  of  a  hollow  stop- cock, 
after  Barnett's  style  of  igniting  arrange- 
ment. With  the  temperature  of  the  mix- 
ture before  ignition  at  12°  Centigrade,, 
the  highest  pressure  attained  was  97  Ibs. 
per  square  inch  above  the  atmosphere. 
The  pressure  was  measured  by  a  loaded 
valve  of  known  area,  as  in  Bunsen' s  -ex- 
periments. The  absolute  pressure  attain- 
ed was  only  about  7-J-  atmospheres  ;  if 
complete  combination  had  taken  placer 


139 

and  no  heat  kept  back  by  dissociation  or 
absorbed  by  change  in  specific  heat,  then 
the  pressure  should  have  been  at  the  low- 
est estimate,  11  atmospheres.  He  con- 
cluded that  Professor  Bunsen's  explana- 
tion of  this  fact  was  a  true  one.  The 
effect  was  equally  visible  in  the  large 
cylinder  used  by  him  and  in  the  small 
tube  used  by  Professor  Bunsen.  These 
experiments,  and  the  recent  experiments 
of  Messrs.  Mallard  and  Le  Chatelier,  make 
it  certain  that  in  a  uniformly  ignited  gas- 
eous mixture  the  temperature  was  limited, 
and  the  apparent  loss  of  heat  was  very- 
slow,  and  that  this  effect  was  due  to  dis- 
sociation, either  complete  or  incipient. 
Such  a  mixture  in  expanding  during  work 
would  give  rise  to  all  the  phenomena  de- 
scribed in  the  paper.  He  was  pleased 
that  his  conclusions  on  the  relation  be- 
tween rate  of  inflammation  at  constant 
pressure  and  constant  volume  had  been 
experimentally  proved  by  these  gentle- 
men. He  had  been  challenged  by  Mr. 
Imray  to  controvert  his  statement  on  the 
history  of  the  introduction  of  the  gas 


140 

engine.  This  he  did  not  do,  because  he 
considered  Mr.  Imray's  account  fairly 
correct. 

The  only  remark  of  Mr.  Imray  on  his 
theory  was :  "  He  would  only  refer  to 
Fig.  9.  If  the  theory  of  dissociation 
were  true,  it  would  follow  that  the  lower 
the  temperature  the  more  dissociation 
would  take  place,  which  was  undoubtedly 
altogether  wrong."  It  was  difficult  to 
understand  this  statement,  it  was  so  ex- 
ceedingly irrelevant.  He  could  hardly 
believe  the  speaker  had  ever  studied  the 
pressure,  volume,  and  temperature  rela- 
tions of  gases.  On  the  indicated  diagram 
low  pressure  had  been  mistaken  for  low 
temperature,  neglecting  the  increased 
volume  due  to  the  travel  of  the  piston. 
Mr,  Imray  had  supposed  that  the  maxi- 
mum pressure  on  line  d  (Fig.  9),  being- 
lower  than  on  line  a,  therefore  the  tem- 
perature was  also  lower.  He  failed  to 
see  the  bearing  on  the  theory  under  dis- 
cussion of  Mr.  Bousfield's  statement : 
"  He  did  not  say  that  when  the  explosion 
took  place,  there  might  not  be  a  certain 


141 

quantity  of  ammonia  and  a  certain  quan- 
tity of  nitric  acid  formed."  The  question 
why,  when  maximum  pressure  was  reach- 
ed at  the  beginning  of  the  stroke,  he  as- 
sumed that  the  flame  had  spread  through- 
out the  mass  in  the  cylinder  was  much 
more  to  the  point.  From  the  original  of 
the  diagram,  Fig.  6,  he  had  taken  the  two 
extreme  lines  shown  at  diagram  Fig.  19,  a 
and  b  were  the  points  of  maximum  pressure. 
In  the  paper  he  had  not  detailed  the  method 
used  to  calculate  the  temperature  attained 
at  the  point  of  maximum  pressure  ;  it  was 
necessary  to  do  so  before  proceeding  fur- 
ther. First,  he  determined  the  exact 
volume  of  the  space  at  the  end  of  the  cy- 
linder into  which  the  mixture  was  com- 
pressed, then  on  the  diagram  he  had 
drawn  the  adiabatic  line  of  compression, 
it  was  the  dotted  line  shown  at  Fig.  6  ; 
the  lower  black  line  was  the  actual  com- 
pression line  drawn  by  the  indicator.  It 
would  be  seen  that  the  two  were  as  near- 
ly as  possible  coincident.  The  cause  of 
this  had  been  pointed  out.  The  temper- 
ature at  the  point  c  was  known  to  be 


142 


Fig.19. 


3347° 


^3311° 

0T^ 


2110° 


l> 


1537° 


Engine  speed  150  revolutions  per  minute. 

One  division  of  circle =one-fiftietli  part  of  a  second  at  above  speed. 


143 

150°.  5  Centigrade,  and  the  pressure  41 
Ibs.  above  atmosphere,  and  assuming  the 
volume  to  remain  constant,  the  tempera- 
ture at  a  was  calculated  from  the  press- 
ure 220  Ibs.  above  atmosphere. 

Let  P  —  pressure  befofe  ignition,  and 
P'  pressure  after  ignition,  T  =  tempera- 
ture before  ignition,  and  T'  temperature 
after  ignition,  then  — 

T,    P'T 


both  pressures  and  temperature  absolute. 
In  diagram  Fig.  1  it  was  shown  that  the 
temperature  of  compression,  correspond- 
ing to  40  Ibs.  above  the  atmosphere,  was 
150°.  5  Centigrade,  and  from  these  figures 
the  temperature  1,537°  was  obtained. 
This  was  the  minimum  possible  tempera- 
ture, as  would  be  observed  from  certain 
considerations  developed  at  p.  21. 
Whether  the  flame  had  spread  through- 
out the  mass  of  the  mixture  or  not,  this 
was  the  average  temperature.  From  a, 
Fig.  19,  was  drawn  an  isothermal  line,  a 
b  c,  dotted  ;  at  the  point  a  the  tempera- 
ture had  commenced  to  fall,  up  to  that 


144 

point  it  had  been  rising  at  a  very  rapid 
rate.  The  semicircle  drawn  below  the 
atmospheric  line  showed  the  path  of  the 
crank-pin,  and  each  division  represented 
in  time  one-fiftieth  of  a  second ;  the  en- 
gine was  running  at  one  hundred  and  fifty 
revolutions  per  minute  when  the  diagram 
was  taken.  Comparing  the  condition  of 
the  gaseous  mixture  in  one-fiftieth  of  a 
second  before  maximum  pressure,  and 
one-fiftieth  of  a  second  after  maximum 
pressure,  in  the  first  one-fiftieth  of  a 
second  the  average  temperature  had  in- 
creased 905°  Centigrade,  while  in  the 
second  hundredth  it  had  diminished  about 
189°  Centigrade.  Within  a  limit  of  one 
twenty-fifth  of  a  second  there  was  a  point 
where  the  increase  of  temperature  ceased, 
and  where  a  fall  of  temperature  began. 
What  did  this  mean  ?  Why  did  the  in- 
crease of  temperature  cease  in  so  sudden 
a  manner  and  a  fall  of  temperature  set 
in? 

From  the  point  d  to  a  the  temperature 
had  been  increasing,  this  increase  being 
due  to  the  progress  of  the  flame ;  at  the 


145 

point  a  the  increase  ceased,  and  a  fall  set 
in.  Take  the  point  6,  then  the  average 
temperature  was  632°  Centigrade  ;  from 
e  to  a  the  time  taken  one-fiftieth  of  a 
second,  and  the  temperature  rose  to 
1,537°  Centigrade ;  in  that  time  it  had 
increased  by  905° ;  suppose  the  same 
rate  of  increase  to  continue  for  another 
one-fiftieth  of  a  second,  the  pressure 
would  rise  to  the  point  /*,  and  the  tem- 
perature would  be  2,442°  Centigrade,  the 
points  g  and  h  showed  the  effect  of  fur- 
ther increase.  But  the  increase  had 
abruptly  ceased  at  the  point  a  ;  from  a  to 
f  the  volume  had  changed  so  slightly  that 
the  rate  of  cooling  could  not  have  in- 
creased appreciably.  The  amount  of ' 
work  done  in  that  movement  was  also 
relatively  insignificant,  and  yet  from  some 
cause  the  increase  of  temperature  going 
on  with  such  rapidity,  905°  in  one-fiftieth 
of  a  second,  had  not  only  diminished,  but 
an  opposite  effect  had  set  in.  It  could 
not  be  supposed  for  a  moment  that  the 
progress  of  the  flame  had  been  abruptly 
stopped  by  any  cause  other  than  com- 


146 

pleted  inflammation  of  the  whole  mass. 
The  flame  which  in  one  instant  of  time 
had  been  flashing  through  the  explosion 
mixture  had  reached  the  enclosing  walls, 
it  had  uniformly  heated  the  whole  com- 
bustible mass,  and  in  the  next  instant  the 
temperature  began  to  fall ;  the  law  of 
cooling  took  effect.  The  very  rapid  rate 
of  rise,  and  the  abrupt  change  from  rapid 
rise  to  slow  fall  of  temperature,  at  a  given 
point,  showed  that  at  that  point  completed 
inflammation  had  been  attained.  The 
cooling  which  was  so  slow  as  to  be  unable 
to  put  an  appreciable  check  on  the  rate  of 
rise  up  to  the  point  of  maximum  temper- 
ature, could  not  be  supposed  to  suddenly 
increase  to  such  an  enormous  extent  as  to 
completely  absorb  and  overpower  at  that 
instant  the  effect  of  continual  spread  of 
flame.  There  could  be  no  doubt  that,  as 
Sir  Thomson  had  pointed  out,  on  diagram 
Fig.  6,  the  maximum  of  the  curve  indicat- 
ed truly  the  instant  when  the  combus- 
tion was  as  complete  as  dissociation 
allowed  it  to  be.  It  was  certain  that  at 
this  point  of  the  diagram  the  flame  had 


147 

spread  completely  through  the  whole 
volume  of  inflammable  mixture,  and  that 
in  whatever  way  the  sustaining  of  the 
pressure  to  nearly  the  adiabatic  line  was 
to  be  explained,  it  could  not  be  accounted 
for  on  the  hypothesis  of  a  continued 
s  read  of  flame. 

A  little  consideration  of  the  conditions 
of  the  indicated  diagram  would  show  that 
the  slower  the  rate  of  inflammation,  rel- 
atively to  the  movement  of  the  piston, 
the  less  distinct  would  the  point  of  maxi- 
mum pressure  become,  and  the  more 
rounded  would  the  apex  of  the  diagram 
appear.  Nevertheless  the  point  of  com- 
pleted inflammation  was  easily,  deter- 
mined from  the  point  of  maximum  tem- 
perature, when  near  the  end  of  the  stroke 
this  point  might  not  be  the  point  of  maxi- 
mum pressure.  He  had  been  careful  to 
make  this  distinction,  and  had  said,  with 
reference  to  slow  inflammation,  p.  25: 
"  This  supposed  phenomena  has  been 
erroneously  called  slow  combustion ;  if  it 
has  any  existence  it  should  be  called  slow 
inflammation.  It  has  a  real  existence  in 


148 

the  Otto  engine  only  when  it  is  working 
badly ;  but  even  then  maximum  tempera- 
ture is  attained,  and  very  distinctly  marks 
the  point  of  completed  inflammation." 
On  diagram  Fig.  19  was  shown  the  effect 
of  increasing  the  speed  of  the  engine 
while  preserving  a  constant  rate  of  in- 
flammation. If  the  speed  were  increased 
from  one  hundred  and  fifty  revolutions 
per  minute  three  times,  or  to  four  hun- 
dred and  fifty  revolutions  per  minute,  it 
would  be  found  that  the  point  a  would 
be  moved  forward  to  k  and  b  to  I.  In 
both  cases  the  temperature  attained 
would  be  nearly  1,537°  Centigrade,  a 
slight  fall  would  be  observed  due  to  in- 
creased cooling  surface  and  to  a  part  of 
the  work  being  done  before  maximum 
temperature  was  attained.  But  in  all 
cases  the  maximum  temperature  marked 
the  point  of  completed  inflammation  and 
the  temperature  began  to  fall  so  soon  as 
it  was  attained.  For  ignitions  attaining 
their  maximum  very  late  in  the  stroke, 
maximum  pressure  need  not  coincide  with 
maximum  temperatures ;  but  a  reference 


149 

to  the  isothermal  line  showed  the  point 
of  highest  temperature.  Using  an  in- 
flammable mixture  of  constant  composi- 
tion, and  varying  the  speed  of  the  engine, 
it  was  always  found  that  ignitions  at- 
tained maximum  temperature  later  and 
later  in  the  stroke  always  came  very  near 
the  isothermal  line  drawn  from  the  point 
of  highest  pressure  at  the  beginning  of 
the  stroke.  The  lines  never  ran  over  this 
isothermal.  This  meant  that,  whether 
inflammation  was  completed  early  or  late 
in  the  stroke,  nearly  the  same  maximum 
temperature  was  attained.  It  followed 
from  the  relations  between  isothermal 
and  adiabatic  lines,  that  the  lines  drawn 
by  the  indicator  from  late  ignitions  always 
crossed  those  from  early  ignitions.  This 
was  shown  by  the  diagrams  taken  from 
an  Otto  engine  by  Mr.  Bousfield,  for 
which  he  must  thank  that  gentleman.  In 
these  diagrams,  however,  it  was  evident 
that  the  mixture  used  had  not  been  of 
constant  composition  at  all  speeds.  This 
would  be  evident  by  examining  Fig.  15. 
When  the  speed  had  been  changed  from 


150 

one  hundred  revolutions  per  minute  in 
the  ]arger  diagram  to  two  hundred  in  the 
smaller,  the  increased  speed  of  the  engine 
had  caused  it  to  take  in  a  smaller  weight 
of  gaseous  mixture,  as  was  shown  by  the 
compression  line  leaving  the  atmospheric 
line  later,  and  that  the  pressure  on  com- 
pletion of  the  in  stroke  only  rose  to  22 
Ibs.  per  square  inch  instead  of  30  Ibs.,  as 
in  the  other.  If  the  mixture  had  been 
the  same  the  point  of  maximum  pressure 
would  have  crossed  in  the  first  diagram 
at  this  point,  and  the  pressure  line  would 
have  run  into  the  first  lower  down,  as 
was  shown  in  his  diagram  at  #,  Fig.  19. 
In  the  Otto  engine  the  hot  exhaust  re- 
maining in  the  space  when  each  cycle  was 
completed  still  further  complicated  the 
comparison  between  different  speeds.  At 
the  higher  speeds  the  walls  of  the  cylinder 
had  less  time  to  cool  the  exhaust,  and 
consequently  the  average  temperature  of 
the  mixture  before  compression  must  be 
greater  at  high  speeds.  In  his  own  gas 
engine  this  complication  had  no  existence, 
because  the  whole  charge  was  replaced  at 


151 

every  stroke.  In  Mr.  Bousefield's  dia- 
gram, Fig.  16,  the  same  change  of  mix- 
ture was  evident,  but  here  the  change  of 
speed  of  the  engine  was  relatively  greater, 
and  consequently  the  lower  diagram 
crossed  the  upper  one  somewhat  earlier. 
In  Fig.  17  this  was  more  and  more  evi- 
dent ;  still  no  two  of  the  compression 
lines  coincided,  showing  the  proportion 
of  exhaust  to  inflammable  mixture  to  be 
continually  increasing,  and  the  maximum 
temperature  attainable  by  the  ignition 
consequently  becoming  less  and  less. 
Even  in  diagram,  Fig.  18,  maximum  tem- 
perature was  attained,  and  could  easily  be 
discovered  by  calculating  the  average 
temperature  at  each  point  along  the  line 
of  increasing  volume.  Mr.  Bousfield 
stated  that  a  light  applied  to  the  exhaust 
of  an  engine,  giving  diagram,  Fig.  16,. 
caused  explosion,  and  from  that  inferred 
that  combustion  was  not  completed  at 
the  end  of  the  stroke.  He  would  find 
that  when  this  happened  the  engine  was 
missing  ignition  altogether  and  discharg- 
ing the  unburned  contents  into  the  ex- 


152 

liaust.  He  might  observe  that  the  hor- 
izontal line  in  that  diagram  did  not 
mean  constant  temperature,  but  indicated 
constantly  increasing  temperature.  Mr. 
Bousfield  has  evidently  fallen  into  the 
same  error  as  Mr.  Imray.  and  confound- 
ed low  pressure  with  low  temperature 
without  considering  the  change  of  vol- 
ume. It  was  a  characteristic  of  the  in- 
flammation of  a  gaseous  mixture  in  mass, 
that  so  long  as  inflammation  continued 
to  spread,  so  long  did  the  average  tem- 
perature increase.  Dissociation  did  not 
begin  to  sustain  temperature  until  the 
temperature  fell.  In  the  construction  of 
the  theoretical  diagram  Mr.  Bousfield 
had  fallen  into  error.  He  drew  from  the 
points  F  G  H,  Fig.  14,  to  A  L  produced, 
lines  which  he  described  as  adiabatics, 
.and  then  said  that  the  curve  drawn 
through  P  Q  R  "represented  the  press- 
ure at  any  time  in  the  contents  of  the 
•cylinder,  supposing  these  contents  remain 
confined  in  the  space  at  the  end  of  the 
cylinder,  and  not  allowed  to  expand." 
the  lines  F  G  H  should  not  be 


153 

adiabatics  but  isothermals,  as  Mr.  Bous- 
field's  object  in  constructing  the  diagram 
was  to  get  the  time  taken  in  a  closed 
space  to  attain  the  temperature  existing 
in  the  engine  at  the  points  F  G  H. 
The  points  L  M  N  should  show  the 
pressure  at  constant  volume  at  these 
temperatures.  If  Mr.  Bousfield  calcu- 
lated the  temperature  from  an  actual 
diagram,  he  would  find  that  maximum 
temperature  coincided  with  maximum 
pressure  when  at  the  beginning  of  the 
stroke.  He  thought  from  his  remaining 
criticisms  that  Mr.  Bousfield  had  not  un- 
derstood the  nature  of  the  proof  advanced 
in  the  paper,  and  that  when  he  had 
studied  the  subject  and  appreciated  the 
nature  of  the  considerations  advanced,  he 
would  admit  the  truth  of  the  theory  set 
forth  in  the  paper. 

It  had  been  asked  by  Dr.  Hopkinson 
whether  the  pressure  rose  higher  when 
an  engine  was  running  slowly  than  when 
it  was  running  fast  ?  Whether  the  press- 
ure attained  on  exploding  a  gaseous  mix- 
ture in  a  closed  space  and  in  an  engine 


154 

was  the  same  ?  Given  the  same  propor- 
tion of  gas  to  air  and  the  same  tempera- 
ture and  pressure  of  mixture  before  igni- 
tion, then  the  pressure  attained  after  ig- 
nition was  the  same  in  all  stages  where 
the  maximum  pressure  was  attained  at 
the  beginning  of  the  stroke ;  it  was  the 
same  whether  in  a  closed  space  or  in  an 
engine.  But  the  ignition  must  be  rapid 
enough  at  the  higher  rate  of  speed  to 
give  maximum  pressure  at  the  beginning 
of  the  stroke.  As  he  had  already  pointed 
out,  if  an  engine  was  to  run  fast  enough 
it  might  overrun  the  rate  of  inflammation, 
and  the  maximum  temperature  would  not 
be  attained  till  towards  the  end  of  the 
stroke.  If  an  engine  was  run  at  two 
hundred  revolutions  per  minute  and  max- 
imum pressure  was  attained  at*  the  begin- 
ing  of  the  stroke,  then  however  slowly 
that  engine  ran  using  the  same  mixture, 
the  maximum  pressure  would  always  be 
the  same,  it  would  not  increase.  Dr. 
Hopkinson  then  asked,  Was  the  maxi- 
mum pressure  the  same  in  large  and  in 
small  engines.?  When  using  a  similar 


155 

mixture,  the  same  pressure  and  tempera- 
ture before  ignition,  it  was  the  same.  In 
small  engines  the  temperature  fell  more 
rapidly  than  in  large  ones  because  of  the 
greater  proportion  of  cooling  surface  to 
volume  of  gases,  but  the  maximum  press- 
ure attained  was  nevertheless  the  same 
because  of  the  rapid  rate  of  ignition.  The 
results  obtained  in  the  large  cylinder  to 
which  he  had  alluded,  and  those  obtained 
by  Professor  Bunsen  in  a  small  tube, 
each  showing  a  limit  to  the  rise  of  tem- 
perature which  could  not  be  referred  to 
cooling,  and  each  showing  complete 
spread  of  flame,  proved  that  the  maximum 
pressure  to  be  obtained  from  an  explosive 
mixture  was  independent  of  the  dimen- 
sions of  the  vessel  used.  Dr.  Hopkinson 
had  asked  why,  in  comparing  types  2  and 
3  of  engine,  he  used  different  maximum 
pressures ;  why  in  the  second  type  he 
used  76  Ibs.  per  square  inch  above  the 
atmosphere,  and  in  the  third  over  200  Ibs. 
per  square  inch.  His  reason  was  this : 
the  three  types  were  taken  under  condi- 
tions which  have  been  found  in  practice 


156 

to  be  the  most  favorable  for  each.  He 
had  compared  the  theory  of  these  types 
of  engine  as  nearly  as  possible  under  con- 
ditions used  in  practice,  It  was  quite 
true  that  type  2  should  be  compared  with 
type  3  under  similar  conditions  of  press- 
ure from  a  purely  theoretic  standpoint ; 
but  the  object  of  the  paper  had  been  to 
inquire  into  the  cause  of  the  greater  effi- 
ciency of  the  third  type  as  in  use  against 
the  two  first  also  in  use.  It  would  be 
seen  that  to  attain  a  pressure  of  200  Ibs. 
per  square  inch  in  type  2  it  was  necessary 
to  compress  the  mixture  to  that  pressure 
before  ignition,  the  temperature  of  com- 
pression being  nearly  o65°  Centigrade. 
This  involved  considerable  loss  of  heat  in 
the  reservoir,  and  increased  the  chances 
of  leakage  while  compressing  ;  in  type  3 
a  pressure  of  40  Ibs.  per  square  inch  be- 
fore ignition  was  all  that  was  required  to 
attain  200  Ibs.  after  ignition.  He  believed 
that  type  2  could  work  advantageously  at 
a  much  higher  pressure  than  76  Ibs.  per 
square  inch,  but  he  questions  whether  it 
could  do  so  at  so  high  a  pressure  as  200 


157 

Ibs.  The  advantage  of  type  3  in  this 
respect  was  a  comparatively  low  pressure 
before  ignition.  With  careful  workman- 
ship doubtless  it  would  be  possible  to  use 
an  engine  of  type  2,  the  theoretical  effi- 
ciency of  which  would  be  quite  as  much 
as  type  3,  as  given  in  the  paper. 

The  description  by  Mr.  F.  H.  Wenham 
of  his  work  on  hot-air  engines  was  inter- 
esting, and  his  distinction  of  the  cylinder 
itself  as  the  heat  generator  or  furnace 
was  the  essential  one  between  gas  and 
hot-aii*  engines,  and  was  indeed  the  great 
cause  of  success  in  these  engines.  Mr. 
H.  Davey  had  objected  to  his  com- 
parison of  the  efficiency  of  gas  and  steam 
engines,  and  considered  the  basis  of  com- 
parison of  efficiency  used  by  him  as  an 
unfair  one.  In  comparing  engines  of  the 
same  system  it  was  right,  as  Mr.  Davey 
stated,  to  use  as  the  standard  the  mechan- 
ical equivalent  of  the  total  available  heat ; 
but  in  engines  of  totally  different  nature 
the  only  basis  of  comparison  was  the 
number  of  heat-units  given  to  the  engine, 
and  the  number  of  these  heat-units  con- 


158 

verted  into  mechanical  work.  If  one  sys- 
tem was  necessarily  limited  in  range  of 
temperature,  as  the  steam  engine  was, 
then  the  inquiry  must  not  be  how  near  it 
approached  perfection  within  that  range, 
but  how  much  heat  could  another  sys- 
tem convert  into  work  as  compared  with 
it.  In  comparing  steam  engines  with 
steam  engines  Mr.  Davey  is  perfectly 
right ;  in  comparing  with  gas  engines  the 
.general  basis  must  be  taken.  He  agreed 
that  the  speedy  downfall  of  the  steam 
engine  was  not  to  be  anticipated ;  he 
only  held  that  the  gas  engine  was  now  in 
its  infancy,  that  it  contained  greater 
possibilities  than  the  steam  engine,  and 
that  in  the  future  it  was  c^-tain  to  be  in 
•every  way  a  great  advance  on  the  steam 
engine,  and  likely  to  supersede  it. 

The  propriety  of  treating  the  gas  en- 
gine as  an  air  engine  had  been  called  in 
question,  and  he  had  been  asked  whether 
the  specific  heats  of  air  and  the  gaseous 
mixture  used  were  in  any  way  comparable. 
The  specific  heat  of  air  at  constant  vol- 
ume was  0.169,  and  the  specific  heat  of  a 


159 

mixture  of  1  volume  of  coal  gas  and  12 
volumes  of  air  could  not  exceed  0.200,  so 
that  for  the  purpose  of  approximate 
comparison  their  adiabatic  curves  might 
be  considered  as  nearly  identical.  So 
little  was  known  of  the  specific  heat  of 
gases  at  high  temperature  that  Mr.  Clerk 
considered  it  simply  an  affectation  of  ac- 
curacy to  endeavor  to  make  the  com- 
parison closer.  He  was  aware  that  the 
efficiency  of  a  heat  engine  was  independ- 
ent of  the  nature  of  the  fluid  employed, 
provided  the  temperatures  between  wliich 
the  engines  worked  were  the  same —that 
was  provided  there  was  the  same  differ- 
ence between  source  and  refrigerator. 
But  this  was  just  where  the  steam  engine 
failed.  Given  equal  amounts  of  heat  from 
the  same  source,  in  the  steam  engine  the 
high  temperatures  could  not  be  utilized, 
because,  first,  a  certain  quantity  of  heat 
had  to  be  expended  to  change  the  phys- 
ical state  of  the  water  ;  and  as  the  steam 
produced  was  rejected  as  steam  all  the 
heat  so  expended  was  lost  for  the  pur- 
pose of  procuring  high  temperature. 


160 

* 
With  air,   on  the  other  hand,  the  same 

quantity  of  heat  from  the  same  source, 
a  much  higher  temperature  was  attained, 
and  consequently  a  greater  range  of  tem- 
perature due  to  work  performed.  The 
use  of  steam  necessitated  a  limited  range 
of  temperature,  and  the  discharge  of  all 
the  heat  used  in  converting  water  from  a 
liquid  to  a  gas.  It  had  been  argued  that 
in  engine  type  2  he  had  over-estimated 
the  efficiency,  and  made  it  greater  than 
was  possible  from  a  perfect  heat  engine 
working  between  the  limits  of  tempera- 
ture used.  Mr.  Bamber  had  fallen  into 
error  by  mistaking  the  limits,  and  in  this 
he  was  not  alone.  This  type  of  engine 
presented  very  interesting  peculiarities  in 
theory,  which,  so  far  as  he  was  aware,  had 
hitherto  been  missed  by  writers  on 
thermo-dynamics.  Although  1,537°  Centi- 
grade was  the  maximum  temperature, 
and  1,089°  Centigrade  the  temperature 
of  discharge  with  the  exhaust,  yet  these 
temperatures  were  not  the  limits  within 
which  the  engine  was  working ;  the  re- 
frigerator, which  was  at  atmosphere 


161 

temperature  17°  Centigrade,  was  being 
used  to  a  certain  extent  without  being 
apparent. 

The  diagram  was  not  a  simple  one ;  the 
efficiency  0.36  was  the  result  of  the  united 
action  within  two  different  limits.  The 
diagram  from  1,537°  Centigrade  to  1,089° 
Centigrade  was  the  same  both  in  types  1 
and  2,  and  working  between  these  limits 
the  maximum  possible-  efficiency  was 
0.247 ;  but  in  type  1  this  efficiency  was 
not  attained,  because  at  1,089°  Centigrade 
the  air  had  not  the  same  density  as  be- 
fore expansion,  and  some  work  had  been 
expended  in  changing  the  volume  to  twice 
its  original  amount.  If  before  heating 
the  air  had  been  compressed  slightly, 
then  heated  to  1,537°  and  expanded  to 
its  original  volume,  and  lowered  in  tem- 
perature due  to  work  done  to  1,089Q,  the 
duty  would  be  0.247.  If  in  type  1  a  con- 
denser were  used,  and  the  temperature 
reduced  to  17°  Centigrade,  the  additional 
work  obtained  would  raise  its  duty  to 
0.247,  without  this  it  remained  at  0.21. 
In  both  types  the  efficiency  between  the 


162 

Kmits  1,537°  Centigrade  and  1,089°  Centi- 
grade was  the  same  ;  but  in  type  2  a  con- 
siderable amount  of  work  was  obtained 
in  the  earlier  part  of  the  diagram,  a  cer- 
tain amount  of  work  was  done  on  in- 
creasing temperature  from  217°. 5  Centi- 
grade to  1,537°,  and  a  considerable  pro- 
portion of  heat  could  be  converted  into 
work  on  an  increasing  temperature,  still 

T  — T 

conforming  to    the    law   — *•= — -   as   the 

maximum  possible  between  the  limits. 

In  type  2,  to  a  certain  extent,  the  re- 
frigerator at  atmosphere  temperature  was 
made  available  in  a  portion  of  the  action, 
and  consequently  a  portion  of  work  done 
on  increasing  temperature,  while  the  latter 
half  of  the  stroke  was  accomplished  on 
falling  temperature.  This  was  the 
reason  why  a  greater  efficiency  was  got 
than  the  apparent  limits  would  allow. 
Mr.  Bamber  then  argued  that  it  made  no 
difference  whether  it  was  necessary  to 
use  an  air  pump  or  not,  if  only  the  same 
quantity  of  heat  were  consumed  and  the 
same  theoretic  efficiency  obtained.  In 


163 

practice  it  made  all  the  difference  ;  the 
great  cause  of  failure  with  hot-air 
engines  was  not  imperfect  theory  but 
very  low  available  pressures  combined 
with  high  maximum  pressures.  Nearly 
all  the  power  indicated  was  used  up  in 
friction ;  in  the  earlier  gas  engines  the 
average  pressures  were  very  low  also. 
The  advantages  of  compression  were  a 
high  available  pressure,  small  cooling 
surfaces,  and  small  loss  by  friction. 
There  the  efficiencies  depended  on  the 
range  of  source  and  refrigeration ;  but 
compression  allowed  all  this  to  be  at- 
tained under  practical  conditions.  It  was 
hardly  necessary  to  explain  that  there  was 
a  certain  maximum  efficiency  for  heat 
engines.  What  he  had  shown  in  this 
paper  was  that  a  greater  proportion  of 
this  was  possible  under  working  con- 
ditions with  compression  than  without. 

The  parallel  by  Air.  Cowper  between 
slow  inflammation  and  imperfect  admis- 
sion of  steam  in  a  cylinder  was  very  just, 
and  illustrates  the  great  loss  of  power 
and  heat  involved  by  imperfect  mixing 


1G4 

of  gas  and  air,  or  by  failing  to  attain 
maximum  pressure  as  soon  after  firing  as 
practicable.  It  was  only  by  a  constant 
application  of  theory  to  practice,  and  a 
constant  testing  of  results  obtained  by 
varying  conditions,  that  he  had  been  able 
to  produce  the  diagram  which  Mr. 
Cowper  approved.  The  amount  of  gas 
consumed  by  his  G-HP.  engine  was  22 
cubic  feet  per  1  HP.  per  hour.  Of  course 
in  cost  this  did  not  stand  comparison 
with  the  coal  used  by  a  large  modern 
steam  engine;  the  steam  engine  had 
greatly  the  advantage ;  but  compared  with 
a  small '  steam  engine  it  was  economical. 
When  gas  was  manufactured  expressly 
for  gas  engines  it  need  cost  but  little 
more  than  the  coal  used  to  produce  it, 
and  as  the  gas  need  not  be  illuminat- 
ing all  the  carbon  might  be  converted 
into  gas.  The  gas  might  be  in  fact  a 
mixture  of  carbonic  oxide  and  hydro- 
gen. 


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WEISBACH.  A  MANUAL  OF  THEORETICAL  ME- 
CHANICS. By  Julius  Weisbach,  Ph.  D.  Trans- 
lated by  Eckley  B.  Coxe.  A.M.,  M.E.,  1,100 
pages  and  902  wood-cut  illustrations.  8vo, 
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FRANCIS.  LOWELL  HYDRAULIC  EXPERIMENTS 
—being  a  Selection  from  Experiments  on 
Hydraulic  Motors,  on  the  Flow  of  Water 
over  Weirs,  and  in  open  Canals  of  Uniform, 
Rectangular  Section,  made  at  Lowell, 
Mass.  By  J.  B.  Francis,  Civil  Engineer. 
Third  edition,  revised  and  enlarged,  with 
23  copper  -  plates,  beautifully  engraved, 
and  about  100  new  pages  of  text.  4to. 
cloth 15.00 

KIRK  WOOD.  ON  THE  FILTRATION  OF  RIVER 
WATERS,  for  the  Supply  of  Cities,  as  prac- 
tised in  Europe.  By  James  P.  Kirkwood. 
Illustrated  by  30  double-plate  engravings. 

4to.  cloth 15.00 

1 


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BANNING.  A  PRACTICAL  TREATISE  OF  WATER 
SUPPLY  ENGINEERING.  Relating  to  the 
Hydrology,  Hydrodynamics,  and  Prac- 
tical Construction  of  Water- Works,  in 
North  America,  With  numerous  Tables 
and  180  illustrations.  By  T.  T.  Fanning, 
C.E.  650  pages.  8vo,  cloth  extra,  ,  $6  08 

WHIPPLE.  AN  ELEMENTARY  TREATISE  ON 
BRIDGE  BUILDING.  By  8.  Whipple,  C.  E. 
New  Edition  Illustrated.  8vo,  cloth,  4  Oi 

MERRILL.  IRON  TRUSS  BRIDGES  FOR  RAIL- 
ROADS. The  Method  of  Calculating  Strains 
in  Trusses,  with  fi  careful  comparison  if 
the  most  prominent  Trusses,  in  reference 
to  economy  in  cotnoinatiou,  etc.,  etc.  By 
Bvt.  Col.  William  E.  Merrill,  U.  8.  A.,  Corps 
of  Engineers.  Nine  lithographed  plates 
of  illustrations.  Third  edition.  4to, 
cloth,  a  ....  5  Of 

SHREVE.  A  TREATISE  ON  THE  STRENGTH  OP 
BRIDGES  AND  ROOFS.  Comprising  the  de- 
termination of  Algebraic  formulas  ^or 
Strains  ir  Horizontal,  Inclined  or  Rafter, 
Triangular,  Bowstring  Lenticular  and 
other  Trusses,  from  fixed  and  moving 
loads,  with  practical  applications  and  ex- 
amples, for  the  use  of  Students  and  En- 
gineers By  Samuel  H.  Slireve.  A.  M.f 
Civil  Engineer.  Second  edition,  87  wood- 
cut illustrations.  8vo,  cloth,  3  5C 

KANSAS  CITY  BRIDGE.  WITH  AN  ACCOUNT  OP 
THE  REGIMEN  OF  THE  MISSOURI  RIVER,— 
and  a  description  of  the  Methods  used  for 
Founding  in  that  River.  By  O.  Chanute, 
Chief  Engineer,  and  George  Morisoii,  As- 
sistant Engineer.  Illustrated  w\la  five 
lithographic  views  and  twelve  plates  of 
plans.  4to,clotb,  .  . 


D.  VAN  NOSTRAND'S   PUBLICATIONS. 

CLARKE.  DESCRIPTION  OF  THE  IRON  RAILWAY 
BRIDGE  Across  the  Mississippi  River  at 
Quincy,  Illinois.  By  Thomas  Curtis  Clarke, 
Chief  Engineer,  With  twenty-one  litho- 
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ROEBLING.  LON.I  AND  SHORT  SPAN  RAILWAY 
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With  large  copperplate  engravings  of 
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DUBOIS.     THE  NEW  METHOD  OF  GRAPHICAL 
STATICS.    By  A.  J.  Dubois,  C.  E.,  Ph.  D.  _ 
60  illustrations.   8VO,  cloth,  .       .       .       .      1  50 

McELROY.  PAPERS  ON  HYDRAULIC  ENGINEER- 
ING. The  Hernpstead  Storage  Reservoir  of 
Brooklyn,  its  Engineering  Theory  and  Results, 
By  Samuel  McElroy,  C,  E.  8vo,  paper,  .  5O 

BOW.  A  TREATISE  ON  BRACING— with  its  ap- 
plication to  Bridges  and  other  Structures 
of  Wood  or  Iron.  By  Robert  Henry  Bow, 
C.  E.  156  illustrations  on  stone.  8vo,  cloth,  1  50 

STONEY.  THE  THEORY  OF  STRAINS  IN  GIRDERS 
—and  Similar  Structures— with  Observa- 
tions on  the  Application  of  Theory  to 
Practice,  and  Tables  of  Strength  and  other 
Properties  of  Materials.  By  Bindon  B. 
Stoney,  B.  A.  New  and  Revised  Edition, 
with  numerous  illustrations.  Royal  8vo, 
664  pp.,  cloth, 12  50 

HENRICI.  SKELETON  STRUCTURES,  especially  in 
their  Application  to  the  building  of  Steel 
and  Iron  Bridges.  By  Olaus  Henrici.  8vo, 
cloth,  1  5O 

KING.  LESSONS  AND  PRACTICAL  NOTES  ON 
STEAM.  The  Steam  Engine,  Propellers, 
&c.,  &c.,  for  Young  Engineers.  By  the  late 
W.  R.  King,  U.  8.  N.,  revised  by  Chief-  i 
Engineer  J.  W.  King,  U.  S.  Navy.  19th 
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i>.    VAN  M>RTRAND'S  PUBLICATIONS. 

AUCHINCLOSS.  APPLICATION  OF  THK  SLIDB 
VALVE  and  Link  Motion  to  Stationary, 
Portable.  Locomotive  and  Marine  Engines. 
By  William  8  Auchincloss.  Designed  as 
a  band  book  for  Mechanical  Engineers. 
With  37  wood-cuts  and  21  lithographic 
plates,  with  copper-plate  engraving  of  the 
Travel  Scale.  Sixth  edition.  8vo,  cloth.  $3  00 

BURGH.  MODERN  MARINE  ENGINEERING,  ap- 
plied to  Paddle  and  Screw  Propulsion. 
Consisting  of  3f>  Colored  Plates,  259  Practi- 
cal WTood-cut  Illustrations,  and 403 pages  of 
Descriptive  Matter,  the  whole  being  an  ex- 
position ot  the  present  practice  of  the  fol- 
lowing tinus:  Messrs  J.  Penn  &  Sons; 
Messrs.  Maudslay,  Sons  <fe  Field;  Messrs. 
James  Watt  &  Co. ;  Messrs.  J.  &  G  Ren- 
me.  Messrs.  R.  Napier  &  Sons-  Messrs  J. 
<te  W  Dudgeon:  Messrs.  Ravenim!  & 
Hodgson  MoNsra  Humphreys  &  Tenant i 
Mr  J.  T.  Rpe.iu-er,  and  Messrs.  Forrester 
&  Co.  By  N  P.  Burgh.  Fngireer.  One 
thick  4to  vol.,  cloth.  $25  oo ;  half  morocco,  3O  OJ 

3ACON.  A  TREATISEON  THE  Ru  HARD'S  STEAM- 
ENGINE  INDICATOR  —  with  directions  for 
its  use.  By  Charles  T.  Porter.  Revised, 
with  notes  and  large  additions  as  devel- 
oped by  American  Practice;  with  an  Ap- 
pendix" containing  useful  formula  and  * 
rules  for  Engineers.  By  F  W.  Bacon.  M. 
E.  Illustrated  Second  edition.  12mo. 
Cloth  $1.00;  morocco,  ...  1  M 

ISHERWOOD  ENGINEERING  PRECEDENTS  FOB 
STEAM  MACHINERY.  By  B.  F.  Isherwood, 
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STILLMAN.  THE  STEAM  ENGINE  INDICATOR 
-anti  the  Improved  Manometer  Steam 
and  Vacuum  Gauged— their  utility  an  dap- 
plication.  By  Paul  Stillinan.  New  edition. 
i2mo,  cloth,  ...  .  1  «*• 

4 


•    L».  VAX  NOSTRAND'S   PUBLICATIONS. 

MacCORD.  A  PRACTICAL  TREATISE  ON  THE 
SLIDE  VALVE,  BY  ECCENTRICS— examining 
by  methods  the  action  of  the  Eccentric 
upon  the  Slide  Valve,  and  explaining  the 
practical  processes  of  laying  out  the  move- 
ments, adapting  the  valve  for  its  various 
duties  in  the  steam-engine.  By  C.  W  Mac 
Cord,  A.  M.,  Professor  of  Mechanical 
Drawing,  Stevens'  Institute  of  Technol- 
ogy, Hobokeu,  N.  J.  Illustrated.  4to, 
cloth $3  00 

PORTER.  A  TREATISE  ON  THE  RICHARDS' 
STEAM-ENGINE  INDICATOR,  and  the  Devel- 
opment and  Application  of  Force  in  the 
Steam-Engine.  By  Charles  T.  Porter. 
Third  edition,  revised  and  enlarged.  Il- 
lustrated. 8vo,  clotli,  .  .  3  50 

McCULLOCH  A  TREATISE  ON  THE  M>^IANI- 
CAL  THEORY  OF  HEAT,  AND  ITS  APPLICA- 
TIONS TO  THE  STEAM-ENGINE.  By  Prof. 
R.  S.  McCulloch,  of  the  Washington  and 
Lee  University,  Lexington,  Va.  8vo, 
cloth 3  50 

VAN  BUREN.  INVESTIGATIONS  OF  FORMU- 
LAS—for  the  Strength  of  the  Iron  parts  of 
Steam  Machinery  By  J.  D.  Van  Buren, 
Jr..  C.  E.  Illustrated.  8vo,  cloth,  .  2  00 

STUART.  How  TO  BECOME  A  SUCCESSFUL  EN- 
GINEER. Being  Hints  to  Youths  intending 
to  adopt  the  Profession.  By  Bernard 
Stuart,  Engineer  Sixth  edition  18rno, 
boards,  .....  50 

SHIELDS.  NOTES  ON  ENGINEERING  CONSTRUC- 
TION. Embracing  Discussions  of  the  Prin- 
ciples involved,  and  Descriptions  of  the 
Material  employed  in  Tunneling,  Bridging, 
Canal  and  Road  Building,  etc.,  etc.  By  J. 
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D.    VAN   NOSTKAXD'S   IMPLICATIONS. 

WEYRAUCH.  STRENGTH  AND  CALCULATION  OP 
DIMENSIONS  OK  IRON  AND  STEEL  CON- 
STRUCTIONS. Translated  from  the  German 
of  J.  J.  Weyrauch,  Ph.  D.,  with  four  fold- 
ing Plates.  12ino,  cloth,  .  .  .  $1  00 

STUART.  THE  NAVAL  DRY  DOCKS  OF  THE 
UNITED  STATES.  By  Charles  B.  Stuart, 
Engineer  in  Chief,  U.  S.  Navy.  Twenty- 
four  engravings  on  steel.  Fourth  edition. 
4to,  cloth,  .  .  .  .  .  6  00 

COLLINS.  THE  PRIVATE  BOOK  OF  USEFUL  AL- 
LOYS, and  Memoranda  for  Goldsmiths, 
Jewellers,  etc.  By  James  E.  Collins. 
18mo|  flexible  cloth, 50 

TUNNER.  A  TREATISE  ON  ROLL-TURNING  FOR 
THE  MANUFACTURE  OF  IRON.  By  Peter  Tun- 
ner  *  Translated  by  John  B.  Pearse. 
With  numerous  wood-cuts,  8vo,  and  a 
folio  Atlas  of  10  lithographed  plates  of 
Rolls,  Measurements,  &c.  Cloth,  .  .  10  00 

GRUNER.  THE  MANUFACTURE  OF  STEEL.  By 
M.  L.  Gruner.  Translated  from  the 
French,  by  Lenox  Sm'ith,  A.M.,  E.M. ; 
with  an  Appendix  on  the  Bessemer  Pro- 
cess in  the  United  States,  by  the  transla- 
tor. Illustrated  by  lithographed  drawings 
and  wood-cuts.  8vo,  cloth,  .  .  .  .  3  50 

BARBA.  THE  USE  OF  STEEL  IN  CONSTRUCTION. 
Methods  of  Working,  A pplviug,  and  Test- 
ing Plates  and  Bars.  By  J.  Barba.  Trans- 
lated from  the  French,  with  a  Preface  by 
A.  L.  Holley,  P.B.  Illustrated.  I2mo,  cloth,  1  50 

SHOCK.  STEAM  BOILERS;  THEIR  DESIGN,  CON- 
STRUCTION, AND  MANAGLMEMT.  ^y  William 
A.  Shock,  Engineer-in- Chief.  U.S.N.;  Chief 
of  Bureau  of  Steam  Engineering,  U.S.  N".  480 
pages.  Illustrated  with  150  woodcuts  and  36 
f'lJl-paere  plates  (20  double).  4to,  illustrated, 

half  morocco 15  00 

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I).   VAX   NOSTRAND'S  PUBLICATIONS. 

WARD.  STEAM  FOR  THE  MILLION.  A  Popular 
Treaties  on  Steam  and  its  Application  to 
the  Useful  Arts,  especially  to  Navigation. 
By  J.  H.  Ward,  Commander  U.  S.  Navy. 
8vo,  cloth.  .  .  $1  00 

CLARK.  A  MANUAL  OF  RULES,  TABLES  AND 
DATA  FOR  MECHANICAL  ENGINEERS. 
Based  on  the  most  recent  investigations. 
By  Thin.  Kinnear  Clark.  Illustrated  with 
numerous  diagrams.  1012  pages.  8vo. 
Cloth ,$7  50;  half  morocco,  .  .  .  .  10  00 

JOYNSON.  THE  METALS  USED  IN  CONSTRUC- 
TION :  Iron,  Steel,  Bessemer  Metals,  etc, 
By  F.  H.  Joynson.  Illustrated.  12mo, 
cloth, 75 

DODD.  DICTIONARY  OF  MANUFACTURES,  MIN- 
ING, MACHINERY,  AND  THE  INDUSTRIAL 
ARTS.  By  George  Dodd.  I2mo,  cloth,  1  50 

PRESGOTT.  FIRST  BOOK  IN  QUALITATIVE  CHE- 
MISTRY. By  Albert  B.  Pi escotfc,  Professor 
of  Organic  and  Applied  Chemistry  in  the 
University  of  Michigan.  12mo,  cloth,  .  .  1  50 

PLATTNER.  MANUAL  OF  QUALITATIVE  AND 
QUANTITATIVE  ANALYSIS  WITH  THE  BLOW- 
PIPE. From  the  last  German  edition.  Re- 
v  i sed  and  enlarged.  By  Prof.  Th.  Richter, 
o  the  Royal  Saxon  Mining  Academy. 
Translated  by  Professor  H.  B.Cornwall. 
With  eighty-seven  wood-cuts  and  lithogra- 
phic plate.  Third  edition,  revised.  568pp. 
HVO,  cloth, 5  00 

PLYMPTON.  THE  BLOW-PIPE  :  A  Guide  to  its 
Use  in  the  Determination  of  Salts  and 
Minerals.  Compiled  from  various  sources, 
by  George  W.  Plyrupton,  C.  E.,  A.  M.,  Pro- 
fessor of  Physical  Science  in  the  Polytech- 
nic Institute,  Brooklyn,  N.  Y.  12mo,  c7oth  1  50 
7 


D.  VAN  NOSTRAND'S  PUBLICATIONS. 

JANNETTAZ.  A  GUIDE  TO  THE  DETERMINATION 
OF  BOCKS  ;  being  ail  Introduction  to  Lith- 
olqgy.  By  Edward  Jaunettaz,  Docteur  des 
Sciences.  Translated  from  the  French  by 
G.  W.  Plymptcm,  Professor  of  Physical 
Science  at  Brooklyn  Polytechnic  Institute. 
12mo,  cloth,  .  .  .  .  .  .  „  .  $1  50 

MOTT.  A  PRACTICAL  TREATISE  ON  CHEMISTRY 
(Qualitative  and  Quantitative  Analysis), 
Stoichioiuetry,  Blowpipe  Analysis,  Min- 
eralogy, Assaying,  Pharmaceutical  Prepa- 
rations Human  Secretions,  Specific  Gravi- 
ties, Weights  and  Measures,  etc.,  etc.,  etc. 
By  Henry  A.  Mott,  Jr.,  E.  M.,  Ph.  D.  650  pp. 
8vo,  cloth; '6  00 

PYNCHON.  INTRODUCTION  TO  CHEMICAL  PHY- 
SICS ;  Designed  for  the  Use  of  Academies, 
Colleges,  and  High  Schools.  Illustrated 
with  numerous  engravings,  and  containing 
copious  experiments,  with  directions  for 
preparing  them.  By  Thomas  Buggies  Pyn- 
chon,  D.  D.,  M.  A.,  President  of  Trinity  Col- 
lege, Hartford.  New  edition,  revised  and 
enlarged.  Crown  «vo,  cloth,  .  .  3  00 

PRESCOTT.  CHEMICAL  EXAMINATION  OF  ALCO- 
HOLIC LIQUORS.  A  Manual  of  the  Constit- 
uents of  the  Distilled  Spirits  and  Ferment- 
ed Liquors  ot  Commerce,  and  their  Quali- 
tative and  Quantitative  Determinations. 
By  Alb.  B.  Prescott,  Prof,  of  Chemistry, 
University  of  Michigan,  I2rno,  cloth,  .  1  60 

ELIOT  AND  STORER  A  COMPENDIOUS  MANUAL 
OF  QUALITATIVE  CHEMICAL  ANALYSIS.  By 
Charles  W.  Eliot  and  Frank  H.  Storer.  Be- 
vised,  with  the  co-operation  of  the  Authors* 
by  William  Ripley  Nichols,  Professor  of 
Chemistry  in  the  Massachusetts  Institute 
of  Technology.  New  edition,  revised  Il- 
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NAG.UET.  LEGAL  CHEMISTRY.  A  Guide  to  the 
Detection  of  Poisons,  Falsification  of  Writ- 
ings, Adulteration  of  Alimentary  and  Phar- 
maceutical Substances ;  Analysis  of  Ashes, 
and  Examination  of  Hair,  Coins,  Fire-arms 
and  Stains,  as  Applied  to  Chemical  Juris- 
prudence. For  the  Use  of  Chemists,  Phy- 
sicians, Lawyers,  Pharmacists,  and  Ex- 
perts. Translated,  with  additions,  includ- 
ing a  List  of  Books  and  Memoirs  on  Toxi- 
cology, etc.,  from  the  French  of  A.  Naquet, 
by  J.  P.  Battershall,  Ph.  D. ;  with  a  Preface 
by  C.  F.  Chandler,  Ph.  D.,  M.  D.,  LL.  D. 
Illustrated.  12nio,  cloth,  .  .  .  .  $2  00 

PRESCOTT.  OUTLINES  OF  PROXIMATE  ORGANIC 
ANALYSIS  for  the  Identification,  Separa- 
tion, and  Quantitative  Determination  of 
the  more  commonly  occurring  Organic 
Compounds.  By  Albert  B.  Prescott,  Pro- 
fessor of  Chemistry,  University  of  Michi- 
gan. 12mo,  cloth,  .  .  .  1  75 

30UGLAS  AND  PRESCOTT.  QUALITATIVE  CHEM- 
ICAL ANALYSIS.  A  Guide  in  the  Practical 
Study  of  Chemistry,  and  in  the  work  of 
Analysis.  By  S.  H.  Douglas  and  A.  B. 
Prescott;  Professors  in  the  University  of 
Michigan.  Third  edition,  revised.  8vo, 
cloth, 3  50 

RAMMELSBERG.  GUIDE  TO  A  COURSE  OF 
QUANTITATIVE  CHEMICAL  ANALYSIS,  ESPE- 
CIALLY OF  MINERALS  AND  FURNACE  PRO- 
DUCTS. Illustrated  by  Examples.  By  C. 
F.  Rammefsberg.  Translated  by  J.  Tow 
ler,  M.  D.  8vo,  cloth 225 

BEILSTEIN.  AN  INTRODUCTION  TO  QUALITATIVE 
CHEMICAL  ANALYSIS.  By  F.  Beilstein. 
Third  edition.  Translated  by  I.  J.  Osbun. 
I2mo.  cloth, 75 

POPE.  A  Hand-book  for  Electricians  and  Oper- 
ators. By  Frank  L.  Pope.  Ninth  edition. 
Revised  and  enlarged,  and  fully  illustrat- 
ed. 8vo,  cloth, 200 


D.  VAN  NOSTRAND'S  PUBLICATIONS. 

SABINE.  HISTORY.  AND  PROGRESS  OF  THE  ELEC- 
TRIC TELEGRAPH,  with  Descriptions  of 
some  of  the  Apparatus.  By  Robert  Sabine, 
C.  E.  Second  edition.  12nu),  cloth,  .  .  $1  25 

DAVIS  AND  RAE.  HAND  BOOK  OF  ELECTRICAL 
DIAGRAMS  AND  CONNECTIONS.  By  Charles 
H.  Davis  and  Frank  B.  Rae.  Illustrated 
with  32  full-page  illustrations.  Second  edi- 
tion. Oblong  8vo,  cloth  extra,  .  .  .  2  00 

HASKINS.  THE  GALVANOMETER,  AND  ITS  USES. 
A  Manual  for  Electricians  and  Students. 
By  C.  H.  Haskins.  Illustrated.  Pocket 
form,  morocco,  .  .  .  .  .  „  „  150 

LARRABEE.  CIPHER  AND  SECRET  LETTER  AND 
TELEGRAPAIC  CODE,  with  Hogg's  Improve- 
ments. By  C.  S.  Larrabee.  18mo,  flexi- 
ble cloth,  1  00 

GILLMORE  PRACTICAL  TREATISE  ON  LIMES, 
HYDRAULIC  CEMENT,  AND  MORTARS.  By 
Q.  A.  Gillmore,  Lt.-Col.  U.  S.  Engineers, 
Brevet  Major-General  U.  S.  Army.  Fifth 
edition,  revised  and  enlarged.  8vo,  cloth,  4  00 

GILLMORE.  COIGNET  BETON  AND  OTHER  ARTIFI- 
CIAL STONE.  By  Q.  A.  Gillmore,  Lt.  CoL 
U.  8.  Engineers,  Brevet  Major-General  U. 
S.  Army.  Nine  plates,  views,  etc.  8vo, 
cloth,  2  50 

GILLMORE.  A  PRACTICAL  TREATISE  ON  THE 
CONSTRUCTION  OF  ROADS;  STREETS,  AND 
PAVEMENTS.  By  Q.  A.  Gillmore,  Lt.-Col. 
U.  S.  Engineers,  Brevet  Major-General  U, 
S.  Army.  Seventy  illustrations.  12mo,  clo.,  200 

GILLMORE.  REPORT  ON  STRENGTH  OF  THE  BUILD- 
ING STONES  IN  THE  UNITED  STATES,  etc. 
8vo,  cloth, 1  00 

HOLLEY.  AMERICAN  AND  EUROPEAN  RAILWAY 
PRACTICE,  in  the  Economical  Generation       C' 
of  Steam.    By  Alexander  L.  Holley.  B.  P. 
With  77  lithographed  plates.    Folio,  cloth,     12  0<? 


D.  VAN  NOSTRAND'S  PUBLICATIONS. 

HAMILTON.  USEFUL  INFORMATION  FOR  RAIL- 
WAY MEN.  Compiled  by  W.  G.  Hamilton, 
Engineer.  Seventh  edition ,  revised  and  en- 
larged. 577  pages.  Pocket  form,  morocco, 
gilt, $2  00 

STUART.  THE  CIVIL  AND  MILITARY  ENGINEERS 
OF  AMERICA.  By  General  Charles  B. 
Stuart,  Author  of  "Naval  Dry  Docks  of 
the  United  States,"  etc.,  etc.  With  nine 
finely-executed  Portraits  on  steel,  of  emi- 
nent Engineers,  and  illustrated  by  En- 
gravings of  some  of  the  most  important 
and  original  works  constructed  in  Ameri- 
ca. 8vo,  cloth 5  00 

ERNST.  A  MANUAL  OF  PRACTICAL  MILITARY 
ENGINEERING.  Prepared  for  the  use  of  the 
Cadets  of  the  U.  S.  Military  Academy, 
and  for  Engineer  Troops.  By  Capt.  O.  H. 
Ernst,  Corps  of  Engineers,  Instructor  in 
Practical  Military  Engineering,  U.  S. 
Military  Academy.  193  wood-cuts  and  3 
lithographed  plates.  I2mo,  cloth,  .  .  5  00 

SIMMS.  A  TREATISE  ON  THE  PRINCIPLES  AND 
PRACTICE  OF  LEVELLING,  showing  its  ap- 
plication to  purposes  of  Railway  Engineer- 
ing and  the  Construction  of  Roads,  etc. 
By  Frederick  W.  Simms,  C.  E.  From  the 
tifth  Ldndon  edition,  revised  and  correct- 
ed, with  the  addition  of  Mr.  Law's  Prac- 
tical Examples  for  Setting-out  Railway 
Curves.  Illustrated  with  three  lithograph- 
ic plates,  and  numerous  wood-cuts.  8vo, 
cloth, .  2  50 

JEFFERS.  NAUTICAL  SURVEYING.  By  William 
N.  Jeffers,  Captain  U.  S.  Navy.  Illustrat- 
ed wiVa  9  copperplates,  and  31  wood-cut 
illustrations.  8vo,  cloth,  .  .  .  5  00 

THE  PLANE  TABLE,   ITS  USES  IN  TOPOGRAPHI-         f 
CAL  SURVEYING.    From  the  papers  of  the 
U.  S.  Coast  Survey.   8vo,  cloth,       .  2  00 


D.   VAN  NOSTRAND'S  PUBLICATIONS. 

A  TEXT-BOOK  ON  SURVEYING,  PROJECTIONS, 
AND  PORTABLE  INSTRUMENTS,  for  the  use 
of  the  Cadet  Midshipmen,  at  the  U.  S. 
Naval  Academy.  9  lithographed  plates, 
and  several  wood-cuts.  8vo,  cloth,  .  .  $2  00 

CHAUVENET.  NEW  METHOD  OF  CORRECTING 
LUNAK  DISTANCES.  By  Win.  Chauvenet, 
LL.D.  8vo,  cloth, 2  00 

BURT.  KEY  TO  THE  SOLAR  COMPASS,  and  Sur- 
veyor's Companion;  comprising  all  the 
Rules  necessary  for  use  in  the  Field.  By 
W.  A.  Burt,  U.  S.  Deputy  Surveyor.  Sec- 
ond edition.  Pocket-book  form,  tuck,  .  2  50 

HOWARD.  EARTHWORK  MENSURATION  ON  THE 
BASIS  OF  THE  PRISMOIDAL  FORMULAE. 
Containing  simple  and  labor-saving  meth- 
od of  obtaining  PrismoidaLCon tents  direct- 
ly from  End  Areas.  Illustrated  by  Exam- 
ples, and  accompanied  by  Plain  Rules  for 
practical  uses.  By  Con  way  R.  Howard, 
Civil  Engineer,  Richmond,  Va.  Illustrat- 
ed. 8vo,  cloth, 1  50 

MORRIS.  EASY  RULES  FOR  THE  MEASUREMENT 
OF  EARTHWORKS,  by  means  of  the  Pr-is- 
moidal  Formulae.  By  Elwood  Morris, 
Civil  Engineer.  78  illustrations.  8vo,  cloth,  1  5rf 

CLEVENGER.  A  TREATISE  ON  THE  METHOD  OP 
GOVERNMENT  SURVEYING,  as  prescribed 
by  the  U.  S.  Congress  and  Commissioner  of 
the  General  Land  Office.  With  complete 
Mathematical,  Astronomical,  and  Practi- 
cal Instructions  for  the  use  of  the  U.  S. 
Surveyors  in  the  Field.  By  S.  V.  Cleven- 
ger,  U.  S-  Deputy  Surveyor.  Illustrated. 
Pocket  form,  morocco,  gilt,  .  .  .  250 

HEWSON.  PRINCIPLES  AND  PRACTICE  OF  EM- 
BANKING LANDS  from  River  Floods,  as 
applied  to  the  Levees  of  the  Mississipi. 
By  William  Hewson,  Civil  Engineer.  8vo, 

cloth, ...      2  00 

12 


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OVERDUE. 

<V!AR    1  UL, 

—  /^«y-ii       1       f1^ 

DEC  27  11 

137 

DEC     4  1938 

oUN     8   1943 

DEC  20  194R 

Aff)f%   - 

«Pill9  J948 

24Mar'59FC 

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